Everything you need to know about the PIKE's Motion Control Damping!- Mtbr.com
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  1. #1
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    Everything you need to know about the PIKE's Motion Control Damping!

    Here's a Motion Control explanation guide. Even the rockshox representatives don't know this stuff. I think RS should be giving people more info about it, then they might be more inclined to consider it when they realize how great it really is...

    I rode the stock spring for a week and was able to get it to not use full travel on jumps by adjusting the floodgate, it makes a huge difference. I weigh 180.

    BTW, anyone who buys the PIKE should break it in good before switching to a harder spring.

    Here's why the fork goes through it travel so easy even with the right spring:

    The floodgate control is exactly like Marzocchi's HSCV (high speed compression valve). It remains closed until there's enough pressure to make it flip open and allow more fluid to flow. The floodgate adjuster on the PIKE allows you to change how much pressure is required to move the valve open. When you have the floodgate totally loose it requires ZERO effort to open it up so adjusting the compression knob to full closed still doesn't do anything to slow down the fork because the floodgate is overiding it and letting too much fluid through, thus no compression damping.

    The floodgate valve is always working whether you have the compresion knob open or closed or anywhere in between. This is why it is considered a high speed comression valve. When you put the fork in lockout mode the compression damper is completely closed, so you are pushing entirely on the floodgate spring valve. This is why the fork maintains the ability to adjust it's SPV type lockout and the pressure reuired to move on bumpb but stay locked for no bobing. YOu have to adjust the floodgate in order to get the desired amount of lockout when the compression knob is closed.

    If you are dirt jumping I would put the floodgate valve completely closed tight, that way the compression damping does it's job in slowing down the fork on hits. You then want to put the compression knob wherever you want, usually halfway.

    When you hit the trails, you want to put the floodgate knob full open and the compression full open if you're not doing any drops. This will make the fork respond incredibly fast no matter what high speed you're riding at.

    Pretty cool huh? The PIKE's motion control is pretty much like a fully adjustable HSCV cartrdige AND a SPV chamber in one unit, but is still more adjustable than both! I also think Motion Control feels and works better than SPV, plus it requires no air.

    The idea behind that red swiss cheese thing in the PIKE's damper is this:

    The compression unit and the floodgate sit at the bottom of that red thingy. The red swisscheese thing is actually a rubber spring that allows for 20mm of plush movement. This make it so that when you lock out the compression attached to the bottom of it, it still is allowed to move 20mm by compressing the rubber piece. This helps give the lockout a better transition from locked to the floodgate valve being forced open on a hit and allowing for fork movement. Very cool idea! Very simple too and light weight!

    The rubber tube does a second task even when the fork isn't locked out. It allows for the compression unit to react quicker to super fast and square edged hits by allowing 20mm of movement without oil being forced through the compression/floodgate unit. This allows for the compression/floodgate enough time to open without any delay in fork compliance. It takes a micro second for the floodgate to open, but the rubber piece reacts instantly thus making it smother on REALLY fast hard square edged hits. This is similar to having a shimmed damping system like TPC. It is also why most people say it feels just as smooth or smoother at high speeds than TPC, HSCV, AND FOX's damping system.

    IMO, the MOTION CONTROL SYSTEM is a very revolutionary concept to biking. You can really tell they thought outside of the box on this one. Not only did they create the most versatile damping system, it;s also lighter, more simple, and cheaper to build than any other comperable system.

    VERY COOL!
    Last edited by MicroHuck; 02-06-2005 at 01:03 PM.

  2. #2
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    Quote Originally Posted by MicroHuck

    If you are dirt jumping I would put the floodgate valve completely closed tight, that way the compression damping does it's job in slowing down the fork on hits.
    Drops and jumps are low speed impacts, not high speed, so either RS is telling you the wrong thing, or the system doesn't work like you are saying.

    I don't doubt the Pike's adjustments work, but if you are going to compare RSs latest product, compare it against the latest marzocchi one, which is TST. For example, my AM1 with adjustable compression blowoff, adjustable progression, lockdown, travel, air-spring, etc...

  3. #3
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    Quote Originally Posted by MicroHuck
    Here's a Motion Control explanation guide. Even the rockshox representatives don't know this stuff. I think RS should be giving people more info about it, then they might be more inclined to consider it when they realize how great it really is...

    I rode the stock spring for a week and was able to get it to not use full travel on jumps by adjusting the floodgate, it makes a huge difference. I weigh 180.

    BTW, anyone who buys the PIKE should break it in good before switching to a harder spring.

    Here's why the fork goes through it travel so easy even with the right spring:

    The floodgate control is exactly like Marzocchi's HSCV (high speed compression valve). It remains closed until there's enough pressure to make it flip open and allow more fluid to flow. The floodgate adjuster on the PIKE allows you to change how much pressure is required to move the valve open. When you have the floodgate totally loose it requires ZERO effort to open it up so adjusting the compression knob to full closed still doesn't do anything to slow down the fork because the floodgate is overiding it and letting too much fluid through, thus no compression damping.

    The floodgate valve is always working whether you have the compresion knob open or closed or anywhere in between. This is why it is considered a high speed comression valve. When you put the fork in lockout mode the compression damper is completely closed, so you are pushing entirely on the floodgate spring valve. This is why the fork maintains the ability to adjust it's SPV type lockout and the pressure reuired to move on bumpb but stay locked for no bobing. YOu have to adjust the floodgate in order to get the desired amount of lockout when the compression knob is closed.

    If you are dirt jumping I would put the floodgate valve completely closed tight, that way the compression damping does it's job in slowing down the fork on hits. You then want to put the compression knob wherever you want, usually halfway.

    When you hit the trails, you want to put the floodgate knob full open and the compression full open if you're not doing any drops. This will make the fork respond incredibly fast no matter what high speed you're riding at.

    Pretty cool huh? The PIKE's motion control is pretty much like a fully adjustable HSCV cartrdige AND a SPV chamber in one unit, but is still more adjustable than both! I also think Motion Control feels and works better than SPV, plus it requires no air.

    The idea behind that red swiss cheese thing in the PIKE's damper is this:

    The compression unit and the floodgate sit at the bottom of that red thingy. The red swisscheese thing is actually a rubber spring that allows for 20mm of plush movement. This make it so that when you lock out the compression attached to the bottom of it, it still is allowed to move 20mm by compressing the rubber piece. This helps give the lockout a better transition from locked to the floodgate valve being forced open on a hit and allowing for fork movement. Very cool idea! Very simple too and light weight!

    The rubber tube does a second task even when the fork isn't locked out. It allows for the compression unit to react quicker to super fast and square edged hits by allowing 20mm of movement without oil being forced through the compression/floodgate unit. This allows for the compression/floodgate enough time to open without any delay in fork compliance. It takes a micro second for the floodgate to open, but the rubber piece reacts instantly thus making it smother on REALLY fast hard square edged hits. This is similar to having a shimmed damping system like TPC. It is also why most people say it feels just as smooth or smoother at high speeds than TPC, HSCV, AND FOX's damping system.

    IMO, the MOTION CONTROL SYSTEM is a very revolutionary concept to biking. You can really tell they thought outside of the box on this one. Not only did they create the most versatile damping system, it;s also lighter, more simple, and cheaper to build than any other comperable system.

    VERY COOL!
    Thanks. All the info I can get on this fork is helpful. It may be the ticket for me and my Heckler. Until now the Fox 36 seemed like what I really wanted, but the price rules it out for at least another season. This could actually work out.

    Where is all this info from if not from Rock Shox?

    Kapusta

  4. #4
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    Good info. I have had the Pike Team version for a couple of months now. I agree that it is a very functional and adjustable fork. I didn't know that the floodgate also functioned when the lockout wasn't activated. Only realy complaint that I have is that it doesn't have an air or spring preload adjustment to fine tune the sag/spring to my weight. I am also curious where the info is comming from if not RS.

  5. #5
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    So ... Correct me if I am wrong ?

    I can adjust the floodgate setting to minimise bob , with a compression setting to stop me bottoming out on drops and jumps ,
    I can then run the fork fully open for trail riding but when i see a jump/drop/climb , I can lock it out. and have the compression and floodgate take over to control the landing or 0 bob in the climb ?

  6. #6
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    Quote Originally Posted by DH_WP
    I can adjust the floodgate setting to minimise bob , with a compression setting to stop me bottoming out on drops and jumps ,
    I can then run the fork fully open for trail riding but when i see a jump/drop/climb , I can lock it out. and have the compression and floodgate take over to control the landing or 0 bob in the climb ?
    yep, pretty much it, in a nutshell.

    i've got a team version, and it works as advertised. though i've rarely used the compression/floodgate stuff other than on a few climbs and some urban so far, it has been great when i have. time will tell; most of the high up, long climbing stuff for me is still wet/snowy.....

    the range of adjustment is pretty wide. so even if you need a little heavier spring, you can run it stiffer with the FG/compression stuff until you can get a new coil in there. a bit of air preload would be nice, but not really needed.
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  7. #7
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    There is no way that the red swiss cheese looking thing is moving 20mm. It is not rubber. It is a 5000 inch/pound plastic spring. You are correct in that the valve is forced open by a hit, but the space between the valve at the bottom and the rod to activate it is very, very small. They used plactic because it doesn't have to compress much (5000 inch/pound is VERY stiff) to activate. The red spring isn't used to absorb any bumps at all.

    I agree that it is light and ingenious. Very simple and very effective.

    -James

    Quote Originally Posted by MicroHuck
    The idea behind that red swiss cheese thing in the PIKE's damper is this:

    The compression unit and the floodgate sit at the bottom of that red thingy. The red swisscheese thing is actually a rubber spring that allows for 20mm of plush movement. This make it so that when you lock out the compression attached to the bottom of it, it still is allowed to move 20mm by compressing the rubber piece. This helps give the lockout a better transition from locked to the floodgate valve being forced open on a hit and allowing for fork movement. Very cool idea! Very simple too and light weight!

    The rubber tube does a second task even when the fork isn't locked out. It allows for the compression unit to react quicker to super fast and square edged hits by allowing 20mm of movement without oil being forced through the compression/floodgate unit. This allows for the compression/floodgate enough time to open without any delay in fork compliance. It takes a micro second for the floodgate to open, but the rubber piece reacts instantly thus making it smother on REALLY fast hard square edged hits. This is similar to having a shimmed damping system like TPC. It is also why most people say it feels just as smooth or smoother at high speeds than TPC, HSCV, AND FOX's damping system.

  8. #8
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    Some more confusion

    So there will be a difference in ride between riding with the fork UNLOCKED and the floodgate to the MAX ... and the fork UNLOCKED and the floodgate to the min ? What would you typicaly use where ?

  9. #9
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    Quote Originally Posted by [email protected]
    There is no way that the red swiss cheese looking thing is moving 20mm. It is not rubber. It is a 5000 inch/pound plastic spring. You are correct in that the valve is forced open by a hit, but the space between the valve at the bottom and the rod to activate it is very, very small. They used plactic because it doesn't have to compress much (5000 inch/pound is VERY stiff) to activate. The red spring isn't used to absorb any bumps at all.

    I agree that it is light and ingenious. Very simple and very effective.

    -James
    Sorry dude...

    YOU ARE SOOOOOOOOO WRONG!

    I suggest you check out www.the-red-pill.com click on PIKE then "forks in action" then click on the video "Motion Control". You will see video of how the spring tube is specificly used for small bump compliance when the fork is locked out, this also equates to a buffer zone for compression damping when the fork isn't locked..

    The plastic/rubber swiss cheese piece is actually very pliable for the first 15-20mm and then ramps up to full out stiff 1mm after that. Try putting the floodgate to full lock and then putting the compression to full lock. You will notice that the fork will go down 20mm+ very easily and then stop, this is the conpression spring tube doing it's thing. Want proof? here ya go, it's all in the pics, in fact I'm showing closer to 23mm of movement.

    JM- I don't know what the heck your problem is. Please try understanding what Motion control does before trying to pretend you know anything about it. You know a lot about MArzocchi, but nothing about RS Motion control. The floodgate has everything to do with how the fork behaves on jumps. See... if you have the floodgate full open and try slowing down the fork on drops with just the compression knob, you won't accomplish anything. This is because the floodgate opens up when the compression get's ANY pressure and bypasses the compression valving, thus no compression damping on large hits. You have to close the floodgate all the way or considerably in order to prevent it from bypassing the compression unit. Pretty simple to understand. That's why you have people asking why their brand new PIke doesn't respond to the damping control, because it comes stock with the floodgate wide open.

    Do you understand what low speed and highspeed compression damping actually means?
    Basicly, the low speed valve is just an adjustable port (can change size of port). The highspeed valve (floodgate) is a spring loaded valve that is forced open when fluid pressures are too great for the ported compression hole. You can adjust how firm the springload is on the floodgate valve, thus changing how the fork reacts to high speed hits.

    When the compression hole is closed (just turn knob 180 degrees) the floodgate valve is forced to take the task of letting fluid through. Since it has a spring loaded tension in it, it requires a certain amount of pressure to push the valve open. You can adjust how much pressure it takes to break the valve open and get regular travel, just like SPV.

    Every adjustment on the PIKE goes from nothing to everything, meaning full range of user adjustment. Just like the AM-1 TST system, you can set it up so that the compression knob is EXACTLY like the TST knob. Put it full open and get no comrpession damping, turn it half way and get good low speed compression damping, turn in half a turn from open and it's closed out and in Stable Platform mode. The thing that I like about Motion Control over TST, is that you can fine tune how the fork reacts in all of the compression settings, you can't do that with TST without changing oil (which is not practical on the trailside).
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    Last edited by MicroHuck; 02-09-2005 at 11:13 PM.

  10. #10
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    Quote Originally Posted by MicroHuck

    Do you understand what low speed and highspeed compression damping actually means?
    Yes, but you don't understand that drops and jumps are low speed impacts, and that rock gardens and roots are high speed, regardless of the actual speed of the bike.

  11. #11
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    Quote Originally Posted by Jm.
    Yes, but you don't understand that drops and jumps are low speed impacts, and that rock gardens and roots are high speed, regardless of the actual speed of the bike.
    ??

    jumps, drops (ie, hucking) are high-speed impacts (at least in regards to SPV/motion control) b/c the fork is moving at a high rate of speed. pedaling, braking, turns, g-outs, etc are considered low-speed impacts b/c the force on the fork is more gradual. so dirt jumps/drops/etc *will* activate the floodgate. haven't had any time on TST, but motion control is sweet.

  12. #12
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    Quote Originally Posted by Jm.
    Yes, but you don't understand that drops and jumps are low speed impacts, and that rock gardens and roots are high speed, regardless of the actual speed of the bike.
    JM- we're not talking about 6 inch drops here...

    Since when is a 4ft+ drop slow speed? You are very confused about what damping means.

    Damping is the fluid controlled resistance to fork movement. How can there be ANY compression damping if there is no resistance to movement? If the compression is set closed to resist movement then that equals pressure no matter how fast of a hit, thus any pressure is going to flip open the floodgate if it set really loose.

    The thing is, you don't even seem to know what the floodgate IS. It can be set to be full loose and require NO pressure to activate it to open, THUS at that point it is a low speed compression valve TOO! You have to turn up the floodgate and tighten it in order for it to only actuate on high speed hits.

    I guess you could call it BOTH a low speed valve AND a high speed valve. You can even set it so that it NEVER opens which is good for big drops.

    JM you are starting to make me laugh every time you post in my threads. You give nothing to help people understand the topic and just keep dishing out the same stuff.. "the AM-1 does this... the AM-1q does that...". How does that help people trying to understand motioncontrol? Plus you are completely oblivious to how "adjustable" motion control works.

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    Am I the ONLY one on this forum who knows how motion control works?

    So far it's just been a lot of people with no clue just making false assumptions without experiencing it first hand...

  14. #14
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    Quote Originally Posted by MicroHuck
    Am I the ONLY one on this forum who knows how motion control works?

    So far it's just been a lot of people with no clue just making false assumptions without experiencing it first hand...
    Well, you have been asked several times in this thread where you are getting your info from, and I am still curious to know. It is not from the web site, and you claim that reps don't know this, so how do you? I watched the clip you are talking about, and it does cover in broad terms the functions you describe, (and confirms your asssertion that the swiss cheese thingy is a sort of spring) though many of your finer details are not mentioned there, such as the floodgate control doing anything when in the "unlocked" mode.

    I am not trying to disagree with you, it's just that it would be good to know whether this is based on knowledge of the design or if it is your interpretation of your experience with the shock. In other words, is what you are saying regarding the floodgate control based soley on your playing around with it? (which would be equally, if not more, valid BTW)

    Kapusta

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    Quote Originally Posted by kapusta
    Well, you have been asked several times in this thread where you are getting your info from, and I am still curious to know. It is not from the web site, and you claim that reps don't know this, so how do you? I watched the clip you are talking about, and it does cover in broad terms the functions you describe, (and confirms your asssertion that the swiss cheese thingy is a sort of spring) though many of your finer details are not mentioned there, such as the floodgate control doing anything when in the "unlocked" mode.

    I am not trying to disagree with you, it's just that it would be good to know whether this is based on knowledge of the design or if it is your interpretation of your experience with the shock. In other words, is what you are saying regarding the floodgate control based soley on your playing around with it? (which would be equally, if not more, valid BTW)

    Kapusta
    I've talked with Angry Asian on this issue. He went directly to the guys who designed the fork for the info on the floodgate valve.

    The rest of my info is from just experimenting with the adjustments extensively.

    Most of the info that RS provides doesn't tell you the whole story of how it works. Even if you ask their public representatives at gear shows, they don't really understand more than what's written in brochures.

    IMO, RS has failed misserably in informing people of what their fork does and how it does it. That's why I'm here trying to help people understand it fully.

    I'm surprised no RockShox employees are on here helping people out. Everyone seems to think I work for them. The fact is, would a RS employee admit to smoking weed? I also live in washington.

    I just noticed that there's TONS of wrong info floating around about Motion Control, like thinking the swisscheese tube isn't there for bumps (that's the only reason it's there). I know the truth so I feel obligated to inform people of it.

    Hope I've been helpfull! Not many people thank me. Instead I just get hate PMs from people calling me a RS employee or saying I'm stupid for thinking a Rcckshox product actually outperforms and out adjusts EVERY other system out there...
    Last edited by MicroHuck; 02-10-2005 at 11:41 AM.

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    I am not sure where you are getting the 23mm of movement, though I agree that you are getting it, I am just not sure what is allowing it. I handled the plastic spring at InterBike and find it hard to believe that it would move that much. Besides, plastic doesn't like to bend that much. The only way that they can get away with using it the way that they do is if it doesn't move that much. Plastic fatigues fairly quickly is that kind of situation. Not the best medium for a spring that has to move a fair amount. I am not commenting on Motion Control, or the lockout. I am only stating that the red plastic spring does NOT move 20mm. Is there another spring in there to allow for that movement? More than likely. Again, does the fork move locked out? Yes, your picture clearly shows that, is it the plastic spring allowing that movement? No way.

    -James

    Quote Originally Posted by MicroHuck
    Sorry dude...

    YOU ARE SOOOOOOOOO WRONG!

    I suggest you check out www.the-red-pill.com click on PIKE then "forks in action" then click on the video "Motion Control". You will see video of how the spring tube is specificly used for small bump compliance when the fork is locked out, this also equates to a buffer zone for compression damping when the fork isn't locked..

    The plastic/rubber swiss cheese piece is actually very pliable for the first 15-20mm and then ramps up to full out stiff 1mm after that. Try putting the floodgate to full lock and then putting the compression to full lock. You will notice that the fork will go down 20mm+ very easily and then stop, this is the conpression spring tube doing it's thing. Want proof? here ya go, it's all in the pics, in fact I'm showing closer to 23mm of movement.

    JM- I don't know what the heck your problem is. Please try understanding what Motion control does before trying to pretend you know anything about it. You know a lot about MArzocchi, but nothing about RS Motion control. The floodgate has everything to do with how the fork behaves on jumps. See... if you have the floodgate full open and try slowing down the fork on drops with just the compression knob, you won't accomplish anything. This is because the floodgate opens up when the compression get's ANY pressure and bypasses the compression valving, thus no compression damping on large hits. You have to close the floodgate all the way or considerably in order to prevent it from bypassing the compression unit. Pretty simple to understand. That's why you have people asking why their brand new PIke doesn't respond to the damping control, because it comes stock with the floodgate wide open.

    Do you understand what low speed and highspeed compression damping actually means?
    Basicly, the low speed valve is just an adjustable port (can change size of port). The highspeed valve (floodgate) is a spring loaded valve that is forced open when fluid pressures are too great for the ported compression hole. You can adjust how firm the springload is on the floodgate valve, thus changing how the fork reacts to high speed hits.

    When the compression hole is closed (just turn knob 180 degrees) the floodgate valve is forced to take the task of letting fluid through. Since it has a spring loaded tension in it, it requires a certain amount of pressure to push the valve open. You can adjust how much pressure it takes to break the valve open and get regular travel, just like SPV.

    Every adjustment on the PIKE goes from nothing to everything, meaning full range of user adjustment. Just like the AM-1 TST system, you can set it up so that the compression knob is EXACTLY like the TST knob. Put it full open and get no comrpession damping, turn it half way and get good low speed compression damping, turn in half a turn from open and it's closed out and in Stable Platform mode. The thing that I like about Motion Control over TST, is that you can fine tune how the fork reacts in all of the compression settings, you can't do that with TST without changing oil (which is not practical on the trailside).

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    Quote Originally Posted by [email protected]
    I am not sure where you are getting the 23mm of movement, though I agree that you are getting it, I am just not sure what is allowing it. I handled the plastic spring at InterBike and find it hard to believe that it would move that much. Besides, plastic doesn't like to bend that much. The only way that they can get away with using it the way that they do is if it doesn't move that much. Plastic fatigues fairly quickly is that kind of situation. Not the best medium for a spring that has to move a fair amount. I am not commenting on Motion Control, or the lockout. I am only stating that the red plastic spring does NOT move 20mm. Is there another spring in there to allow for that movement? More than likely. Again, does the fork move locked out? Yes, your picture clearly shows that, is it the plastic spring allowing that movement? No way.

    -James

    I understand what you're saying. There must be something else giving the movement right?

    Not really. When the compression isn't locked out the first two inches of travel are VERY plush and don't require much force at all to push it down. When I put the compression and floodgate to full locked is stiffnes up a bit, thus telling me that the compression unit is blocking oil. Since the compression unit isn't allowing any fluid to flow AND it's located at the bottom of the spring tube, there's only one place you can get movement. That being the MC spring tube. Why would RS put that in there if it wasn't designed to take any movement? They even state that that is exactly why it's there, to give "some" small bump compliance when locked out and to make for a nice transition in the platform breaking loose.

    Next time I open my fork for an oil change, I will document how much the spring tube actually bends to pressure. That's the only true way to tell, but from my deductive observations, the MC spring tube does allow for up to 20mm of travel. After that though the MC unit turns full out rigid and doesn't move.

    I think that is why they made it with swisscheese looking holes. Those holes allow for a specific amount of movement. When the thing compresses to a certain point, those holes close up and thus no more compliance. Makes sense if you think about it...

  18. #18
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    I'm with you JM. Drops and jumps are lower speed high amplitude impacts than rocks & ruts, which are low amplitude high speed impacts.
    "I've come to believe that common sense is not that common" - Matt Timmerman

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    MicroHuck, I have held the spring tube. It doesn't move that much. I have tried to compress it while it was out of the fork. I can tell you exactly what it does. It is the spring that keeps the floodgate from activating all the time. I don't have pictures so I know that I am not making myself clear. There is a rod from the valve and a rod from the adjuster. These two rods don't meet. How much they don't meet is up to the adjuster. When a bump is hit with sufficient force, the spring tube deflects a very small amount and the rods meet, forcing the valve open. Elegantly simple and very effective. Please, do take a look at it when you have it apart next. It is very simple and very well engineered. If only they made one without a through axle.

    -James

    one more thing, I believe that the spring is in the other leg. There aren't springs in both legs.

    Quote Originally Posted by MicroHuck
    I understand what you're saying. There must be something else giving the movement right?

    Not really. When the compression isn't locked out the first two inches of travel are VERY plush and don't require much force at all to push it down. When I put the compression and floodgate to full locked is stiffnes up a bit, thus telling me that the compression unit is blocking oil. Since the compression unit isn't allowing any fluid to flow AND it's located at the bottom of the spring tube, there's only one place you can get movement. That being the MC spring tube. Why would RS put that in there if it wasn't designed to take any movement? They even state that that is exactly why it's there, to give "some" small bump compliance when locked out and to make for a nice transition in the platform breaking loose.

    Next time I open my fork for an oil change, I will document how much the spring tube actually bends to pressure. That's the only true way to tell, but from my deductive observations, the MC spring tube does allow for up to 20mm of travel. After that though the MC unit turns full out rigid and doesn't move.

    I think that is why they made it with swisscheese looking holes. Those holes allow for a specific amount of movement. When the thing compresses to a certain point, those holes close up and thus no more compliance. Makes sense if you think about it...

  20. #20
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    Quote Originally Posted by [email protected]
    MicroHuck, I have held the spring tube. It doesn't move that much. I have tried to compress it while it was out of the fork. I can tell you exactly what it does. It is the spring that keeps the floodgate from activating all the time. I don't have pictures so I know that I am not making myself clear. There is a rod from the valve and a rod from the adjuster. These two rods don't meet. How much they don't meet is up to the adjuster. When a bump is hit with sufficient force, the spring tube deflects a very small amount and the rods meet, forcing the valve open. Elegantly simple and very effective. Please, do take a look at it when you have it apart next. It is very simple and very well engineered. If only they made one without a through axle.

    -James

    one more thing, I believe that the spring is in the other leg. There aren't springs in both legs.
    OK, I'll give you that. One thing I don't get though.

    Have your ever had a fork spring in your hand? It's pretty much impossible to compress a fork spring by hand, yet can feel very plush when you put it into a fork and lean on it.

    There's a HUGE difference between arm strength and 180 lbs of body weight. I would agree with you on one thing, the plastic tube must be hard to bend with just your hands (just like a coil spring).

    I'm still interested in where that 20mm is coming from, so I guess I'll just have to wait and check it out next time I open the fork.

    Regardless of your own personal oberservations, rockshox claims that the spring tube was placed into there for small bumps when locked out. How else would they achieve 20mm of compliance when the fork is locked? That's what I want to know...

  21. #21
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    The 20 mm has to come from another spring. I don't have a cut away with me of the fork. I'll go through my literature this evening (i don't have it with me) and see if I can answer some of your questions.

    Yes, I have tried to compress a coil spring outside of a fork. You are correct that it is hard. I have tried to compress an MCU stack, and that, too, was very hard. This is a whole different level. I don't have a Pike in my possession. In fact, InterBike was the last time I saw one. I just know that the plastic spring is NOT the main spring.

    The reason they might claim that it is for small bump compliance (warning: I am moving into the relm of speculation here so take it with a grain of salt) is that it allows Rock Shox to separate small hit compliance from the big hits. The plastic spring would only activate on big hits (how big depends on the settings), but another system, with other settings, would be active on the small stuff.

    Again, I will try and dig up a cut-away of the fork. I really am not trying to be confusing, but I don't have an image at hand that shows what I am trying to say.

    -James

    Quote Originally Posted by MicroHuck
    OK, I'll give you that. One thing I don't get though.

    Have your ever had a fork spring in your hand? It's pretty much impossible to compress a fork spring by hand, yet can feel very plush when you put it into a fork and lean on it.

    There's a HUGE difference between arm strength and 180 lbs of body weight. I would agree with you on one thing, the plastic tube must be hard to bend with just your hands (just like a coil spring).

    I'm still interested in where that 20mm is coming from, so I guess I'll just have to wait and check it out next time I open the fork.

    Regardless of your own personal oberservations, rockshox claims that the spring tube was placed into there for small bumps when locked out. How else would they achieve 20mm of compliance when the fork is locked? That's what I want to know...

  22. #22
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    Quote Originally Posted by MicroHuck
    JM- we're not talking about 6 inch drops here...

    Since when is a 4ft+ drop slow speed? .
    Since the speed of the fork moving up and down was relatively slower on a drop or jump as compared to when you ride through an impact and the fork has to move up and down faster, which would be a root or rock.

    You seem to have a general lack of knowledge in this area. You should stop while you are behind.
    Last edited by Jm.; 02-10-2005 at 07:13 PM.

  23. #23
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    Quote Originally Posted by Jm.
    Since the speed of the fork moving up and down was relatively slower to when you ride through an impact and the fork has to move up and down faster.

    You seem to have a general lack of knowledge in this area. IYou should stop while you are behind.
    Doesn't this guy annoy the phuck outta you? He thinks he knows everything, yet lacks some very basic knowledge.

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    Hey JM, i'm in agreement with everyone else here. High speed dampening refers to how fast the fork or shock blows through its travel. The impact caused from a 4 ft drop causes the fork to go through the majority of its travel very fast. I think where your confused is when thinking about how quickly the fork prepares it's self for the next hit. This has nothing to do with High or Slow speed dampening this refers to the rebound dampening causing the fork to follow the contours of a trail.

    In the end:

    Big hit = High Speed Dampening (blows through travel at a HIGHSPEED)
    Small bumps = Slow Speed Dampening (go's through travel at a SLOW SPEED)
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  25. #25
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    Quote Originally Posted by drum714
    Hey JM, i'm in agreement with everyone else here. High speed dampening refers to how fast the fork or shock blows through its travel. The impact caused from a 4 ft drop causes the fork to go through the majority of its travel very fast. I think where your confused is when thinking about how quickly the fork prepares it's self for the next hit. This has nothing to do with High or Slow speed dampening this refers to the rebound dampening causing the fork to follow the contours of a trail.

    In the end:

    Big hit = High Speed Dampening (blows through travel at a HIGHSPEED)
    Small bumps = Slow Speed Dampening (go's through travel at a SLOW SPEED)
    Then you are only in agreement with one person.

    The impact from a 4 ft drop causes the fork to go through it's travel much slower compared to how fast the fork has to move when you hit a rock or root out on the trail.

    This has everything to do with the high and low speed damping.

    Sorry.

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    Upset Enough already!!!!!!

    Ok, here's the deal with the spring tube: Yes, even without allowing oil through the piston, it DOES allow for about 20mm of fork movement. You are all forgetting that 20mm of fork movement does NOT equal a 20mm change in oil height. As the fork moves through its travel, the damper shaft enters into the oil chamber, shrinking the internal volume of that chamber which causes the fluid level to rise. However, the damper shaft has a much smaller diameter than the oil chamber (and hence, a fairly small volume), so 20mm of damper shaft movement only raises the oil level by maybe about 1/4 of that (I'd have to measure the OD of the shaft vs. the ID of the chamber to be sure).

    Microhuck: I can appreciate your enthusiasm for RS' Motion Control setup (it really is quite slick), but you've got some details mixed up a little bit. I don't remember this conversation specifically (sorry, I get A LOT of emails), but while we might have talked about 20mm of movement while the fork was locked out, I certainly never said that the spring tube itself moved that much. Think about it; that thing is made of fairly rigid plastic. While it is designed to be a "spring" to a certain extent, that much strain would certainly result in at least SOME permanent deformation.

    Anyway, I'm not even going to get involved in this low-speed vs. high-speed argument!

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    Last edited by angryasian; 02-10-2005 at 10:16 PM.

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    Trying...to...resist...getting...involved..in...th read....



    Like Jm said, a small hit does not necessarily equate to slow speed damping and large hits don't always equate to high speed damping. In fact, the size of the bump has little to do with the damper circuits used.

    The shape of the bump, regardless of size, has more effect on damper speed. A square-edge 1" high bump can create a faster damper speed than a 1" roller. The square edge 1" bump would quickly overwhelm the low-speed damper circuit and engage the high-speed damping circuit.

    A 1' tall roller might not even engage your suspension, depending on your low-speed damping settings.

    This is just some basic background info to clarify the high-speed and low-speed damping thing. Someone else can jump in here to correct me.

    Quote Originally Posted by drum714
    Hey JM, i'm in agreement with everyone else here. High speed dampening refers to how fast the fork or shock blows through its travel. The impact caused from a 4 ft drop causes the fork to go through the majority of its travel very fast. I think where your confused is when thinking about how quickly the fork prepares it's self for the next hit. This has nothing to do with High or Slow speed dampening this refers to the rebound dampening causing the fork to follow the contours of a trail.

    In the end:

    Big hit = High Speed Dampening (blows through travel at a HIGHSPEED)
    Small bumps = Slow Speed Dampening (go's through travel at a SLOW SPEED)
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    Angryasian, thanks for chiming in here, I was hoping that you would. I went to you sight, but could not find your initial comments on the new forks. Did you take it down?

    -James

    Quote Originally Posted by angryasian
    Ok, here's the deal with the spring tube: Yes, even without allowing oil through the piston, it DOES allow for about 20mm of fork movement. You are all forgetting that 20mm of fork movement does NOT equal a 20mm change in oil height. As the fork moves through its travel, the damper shaft enters into the oil chamber, shrinking the internal volume of that chamber which causes the fluid level to rise. However, the damper shaft has a much smaller diameter than the oil chamber (and hence, a fairly small volume), so 20mm of damper shaft movement only raises the oil level by maybe about 1/4 of that (I'd have to measure the OD of the shaft vs. the ID of the chamber to be sure).

    Microhuck: I can appreciate your enthusiasm for RS' Motion Control setup (it really is quite slick), but you've got some details mixed up a little bit. I don't remember this conversation specifically (sorry, I get A LOT of emails), but while we might have talked about 20mm of movement while the fork was locked out, I certainly never said that the spring tube itself moved that much. Think about it; that thing is made of fairly rigid plastic. While it is designed to be a "spring" to a certain extent, that much strain would certainly result in at least SOME permanent deformation.

    Anyway, I'm not even going to get involved in this low-speed vs. high-speed argument!

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  29. #29
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    Well actually every impact rolls along the damping curve and back again. From stationary to it's max then back to zero.

    The size/shape of the bump determines the max speed and how fast it gets there.
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  30. #30
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    Quote Originally Posted by MicroHuck
    Am I the ONLY one on this forum who knows how motion control works?

    So far it's just been a lot of people with no clue just making false assumptions without experiencing it first hand...
    Motion control works much the same way the original Mag-20's damper worked, and how Amp thrushaft frame shocks worked, Romic twin-tube shocks, and a host of other past fork/shocks, with a mechanical spring loaded high-speed compression valve. The way they handle the spring to hold the valve shut is innovative, but the concept is well proven and tested.

    Romic and Amp use a small coil-spring to keep the valve closed, and restrict fluid (in the case of Amp it was either ATF fluid, or Shell Spindle oil) thru and thus damper shaft movement until the fluid pressure exceeds the valve spring pressure. Pedal forces are low-speed movements, while landing jumps are high speed type impacts. That's one reason why Amp's were loved by mag writers for pedalling so well while at the same time blasted by mag writers for being harsh riding on small low-speed impacts. Later model amp's (around 97 thru 2000) got an adjustable spring for their compression valve, allowing the rider to tune it a bit as to how sensitive it'd be to pedal/low-speed impacts.

    Mag-20/30 forks also used a coil-spring to keep their compression valve closed, and the spring was preloaded by a six-position adjuster on top of each fork leg. Again, this altered how quickly the fork's HSCV would open to an impact (or respond to rider induced bobbing), and could be run almost fully locked out, but would still blow open on a sufficiently large impact. The later Mag-21/10 models (which replaced the 20/30 respectively) added a coil-negative spring, to help pull the compression valve open partially so it'd respond to small impacts faster, while still resisting bobbing to a large degree. I suppose they saw that as an easier fix to implement than having to put a lot of thought and testing into adjusting the port sizes for the oil-flow.

    As to the red swiss-cheese, one of the mag reviews says its a 3000 inch-pound elastomer spring but didn't indicate how far it actually compresses, but I would think its at most 2mm, not 20mm. Why? There's 25.4mm to an inch... for it to compress 20mm would take about a 2400 pound impact force. THAT'S NOT GOING TO HAPPEN !!!! Most XC fork springs rarely need more than 200 inch-pounds to support a rider. DH forks? A bit more but not THAT much more because the spring rates ramp up after the first inch and there's compression damping also.
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  31. #31
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    Quote Originally Posted by Jm.
    Then you are only in agreement with one person.

    The impact from a 4 ft drop causes the fork to go through it's travel much slower compared to how fast the fork has to move when you hit a rock or root out on the trail.

    This has everything to do with the high and low speed damping.

    Sorry.
    Have you ever landed a 4 foot drop? There's nothing particularly slow about damper compression. Someone earlier in the thread pointed out its not a 6" drop... Marzocchi incorporates HSCVs into their upper model DH and BigHit forks for a reason... folks landing big air need HSCV, even the ones just doing wheelie drops.
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  32. #32
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    Quote Originally Posted by DeeEight
    Have you ever landed a 4 foot drop? There's nothing particularly slow about damper compression.
    actually there is, compared to how fast the fork moves up and down in a rock garden. I realize this may be beyond some people's comprehension, but it's the reason why a Jr T or dropoff feels quite "plush" while doing a drop or jump, but why they start to feel like crap on the trail when you get to choppy bumps or roots...

    forks bottom on low speed hits like drops and jumps because the oil passes through the "bleed" for the most part, instead of through the high speed compression valve, this is why you can be riding along at mach 5 and hit a rock, and the fork does not bottom, but why you do a 6 foot to flat drop at 3mph, and the thing slams against the bottom. The reason is that your high speed compression damping takes care of the sharp hits, and the low speed damping takes care of the impacts that cause the fork to move at a slower speed, but both kinds of impacts can produce bottom-out if they do not work correctly.

  33. #33
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    Something about 9.8 m/sec squared.....

    Or 32 ft/sec squared. 4' drop isn't very fast....

  34. #34
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    I think part of the confusion is that shock manufacuterer's marketing departments have been selling the idea that low speed is in the range of pedal bob and brake dive. those speeds are REALLY slow. It may be easier to explain if you called drops and jumps medium speed shaft movements.

    Has any of you seen a shock stroked on a dyno at 30 in/sec, or 60 in/sec? It's so damn fast, it's incomprehensible that an electro-magnetic dyno can accelerate all that mass (most is in it's own ram) against the force of the shocks damping to that velocity, hold it throughout a measureable part of its storke, and stop it again befrore catastrophically crashing the shock into millions of pieces. When you see a 30 in/sec test you think, "Holy sh*t that's fast!", and then when it hits 60, you run out of adjectives to describe it. I don't have ride data on MTB shaft speeds, but MX have been measure to hit 100in/sec or sometimes a little bit faster on hard ruts/whoops...
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  35. #35
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    Actually the spring loaded valve on the romic is on the compression bypass. The main circult is a dished shim stack which opens when the forces get high enough.

    It's all a similar prinicple though.

    Quote Originally Posted by DeeEight
    Motion control works much the same way the original Mag-20's damper worked, and how Amp thrushaft frame shocks worked, Romic twin-tube shocks, and a host of other past fork/shocks, with a mechanical spring loaded high-speed compression valve. The way they handle the spring to hold the valve shut is innovative, but the concept is well proven and tested.

    Romic and Amp use a small coil-spring to keep the valve closed, and restrict fluid (in the case of Amp it was either ATF fluid, or Shell Spindle oil) thru and thus damper shaft movement until the fluid pressure exceeds the valve spring pressure. Pedal forces are low-speed movements, while landing jumps are high speed type impacts. That's one reason why Amp's were loved by mag writers for pedalling so well while at the same time blasted by mag writers for being harsh riding on small low-speed impacts. Later model amp's (around 97 thru 2000) got an adjustable spring for their compression valve, allowing the rider to tune it a bit as to how sensitive it'd be to pedal/low-speed impacts.

    Mag-20/30 forks also used a coil-spring to keep their compression valve closed, and the spring was preloaded by a six-position adjuster on top of each fork leg. Again, this altered how quickly the fork's HSCV would open to an impact (or respond to rider induced bobbing), and could be run almost fully locked out, but would still blow open on a sufficiently large impact. The later Mag-21/10 models (which replaced the 20/30 respectively) added a coil-negative spring, to help pull the compression valve open partially so it'd respond to small impacts faster, while still resisting bobbing to a large degree. I suppose they saw that as an easier fix to implement than having to put a lot of thought and testing into adjusting the port sizes for the oil-flow.

    As to the red swiss-cheese, one of the mag reviews says its a 3000 inch-pound elastomer spring but didn't indicate how far it actually compresses, but I would think its at most 2mm, not 20mm. Why? There's 25.4mm to an inch... for it to compress 20mm would take about a 2400 pound impact force. THAT'S NOT GOING TO HAPPEN !!!! Most XC fork springs rarely need more than 200 inch-pounds to support a rider. DH forks? A bit more but not THAT much more because the spring rates ramp up after the first inch and there's compression damping also.
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  36. #36
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    My point was this..

    The floodgate valve actually acts as a low speed compression blowoff when set loose. It needs to be tightened in order to act as a highspeed valve. That's it. That's why people HAVE to turn up floodgate in order to maintain compression damping on drops. JM just thought that the floodgate was ONLY a high speed valve, but it's actually an adjustable high OR low speed valve depending on setup. It's yet another reason the system is so incredibly adjustable.

    I would think angy asian would agree with me on that. Thanks for clarifying that A A. I was thinking maybe the compression unit creates an air pocket that get's trapped under lockout. Maybe that's where I'm getting the 20mm from? Makes sense.If it does turn out that the plastic tube doesn't need to bend as much then that's a good thing.


    On the note of fast and slow hits...

    You really can't make a blanket statement about what low and high speed means to every fork. Every fork with high speed abilities has it's high speed valving/shimming set to a different level. The only thing a high speed unit does is increase the size of the hole in which oil is forced through when the pressures raise to a certain level. Some forks have the high speed valve/shims set up with a high tolerance to oil pressures and thus have a larger high speed threshold. Other forks have a smaller gap between high speed and low speed valving, meaning you don't have to create much excess pressure in order to flip open the high speed valves.

    You guys are wrong in saying a 4 ft drops is low speed to all forks. Some HSCV Marzocchi forks would blow open the HSCV valve on a fast 4 ft drop to flat. This has everything to do with how large the differential is between low speed damping and the pressure required to make a larger oil hole (higher speed). It this regard it's pointless to argue the whole fast/slow thing. I think we can all agree that a fork moves MUCH faster when doing a drop than when someone makes it bob by pedaling. It all depends on how a fork is set up that determines what it's high speed threshold is.

    The PIKE can be set so that it's high speed threshold is ZERO, thus making the floodgate a low speed valve because it doesn't require really any extra oil pressure to flip it open. It can also be setup so that there's a HUGE differential between the two, which results in the fork needing to be hit really hard and fast in order to actuate the high speed valve.

    My point is this. You can't make a statment about what speed is considered high speed to all fork setups. All high speed means is that it's HIGHER than low speed, HOW MUCH is the real question. There's no question that a 4ft drop is Higher speed than just rolling along a trail, thus technically YES a 4ft drop is a HIGHER speed movement to just about ALL FORKS.

    You guys who are saying you know how to define high speed are going about it all wrong. The point is that high speed damping actually means, "HIGHER SPEED DAMPING", because every fork is different.

  37. #37
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    Quote Originally Posted by TheSherpa
    Doesn't this guy annoy the phuck outta you? He thinks he knows everything, yet lacks some very basic knowledge.

    -TS
    No wonder so many people hate you on this forum. I've never read a single thread where you contributed anything usefull to the topic. I'm not trying to start anything, and for all I know you're a cool guy. Just be a little more on topic and helpfull next time you wish to post.

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    i agree with JM. as far as i know landing a drop-off or summit is low speed compared to what you get when flying down a trail or fire road at high speed and hit a square edged object.
    Marz use HSCV in the higher end forks because its a better system and means that people wanting to do downhill aswell as freeride wont spike to **** whenever they do...... no one would pay that sorta money for a fork with SSV in it.

    Microuck some of your comments make you sound like your digging a hole now, especially with all the "high speed means higher than low speed" and "it depends o the fork what high and low speed is" (note: not exact quotes) ..... eh? low speed contains a range of speeds as does high speed.... and id have though theres a general consensus as to what equates to high speed, roughly atleast.
    Im not expert though, infact far from it but it just makes sense.

    Good info on the Pike though, i was seriously considering getting one before plumping for the AM1 but i decided that for an extra £70 (got a great deal on the AM1s) i would prefer not having to fiddle to setup the fork to get the same sorta setting as the AM switch would allow..... and the fact that i dont need travel adjust and ETA works a treat for steep climbs.
    If i got a 5/6" full susser i think the pike would be my first choice for a fork now though with its bolt through.

  39. #39
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    He's way too confused to try and correct now, I have given up.

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    Quote Originally Posted by Jm.
    He's way too confused to try and correct now, I have given up.
    No you guys are way confused. How hard is it to understand that not all forks have the same fork movement speed required to open the high speed valving? Fork speed directly effects the pressures of oil in the fork, it's the pressures that really determine what happen with the management of oil. Nothing I have said about the floodgate being a valve that determines how "fast" a high speed hit needs to be in order to activate and allow for more fluid movement, has been false.

    What you guys are trying to say is that EVERY fork is setup to register high speed fork movement AT EXACTLY THE SAME LEVEL! You couldn't be any more WRONG. I seriously doubt a Marz HSCV valve is set to open at exactly the same pressures other comperable systems are tuned to. One system might require a higher pressure (thus requiring faster/harder movement to be considered high speed) and another system might require lower pressure (thus requiring lower speed/pressure to activate its high speed ability). Are you seriously going to deny that this is true?

    What you're trying to do is argue that there's some magical speed that EVERY fork must attain in order to be considered high speed. The fork could care less about that "fake" number. All a fork cares about is how much pressure is required to open up and allow more fluid to flow, that's it. That's why Motion Control can be setup to recognise even the slightest increase in fork velocity as being a "higher" speed hit.

    I think you guys are the ones confused about what High and Low speed actually means to a fork (and different forks for that matter). You ever wonder why people complain about HSCV forks blowing through too much travel on drops? It's because the high speed valving is being forced to override the slow speed holes, thus less compression damping, thus more fork movement, thus using tons of travel. Those forks rely on the ramp up of air into the oil level to prevent bottoming from blowing through travel.

    Ideally speaking a fork with large enough of a SSV hole and light enough of an oil would out perform ANY high speed differentiating unit on the market today, AT ANY HIGH SPEED! Systems like HSCV and TPC are designed to give you good low speed damping ALONG with good high speed damping. This can only be accomplished by having two stanges of holes for oil to flow through. You can babble on about shimms and rods and spring valve all you want, but in the end all they are are just a hole for regulating oil flow. You have a small oil hole for good low speed compression control, then you also have a shimmed or spring loaded oil hole that opens up under certain pressures to give you a LARGER oil hole. There's nothing more to it than that, no matter what high end system you're talking about. If you created a SSV hole that was the same size as having BOTH high speed and low speed holes open from a HSCV cart., you would get the same level of high speed bump compliance because you are regulating the same amount of oil. In actuallity though the large SSV hole would out perform the HSCV because there's no shims or spring valves that need to be moved in order to activate, thus the SSV will react quicker (given that it's large enough).

    The problem is that you can't get any good low speed compression control with a giant SSV hole, thus the fork can only be setup to perform well in one type of speed. Marzocchi tries to make their SSV forks somewhere in the middle ground of high speed and low speed, so instead of switching to a larger hole, you are forced to use lighter oil for more high speed comlpliance (whatever high speed actually is to you).
    Last edited by MicroHuck; 02-12-2005 at 12:16 PM.

  41. #41
    Jm.
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    Quote Originally Posted by MicroHuck

    What you guys are trying to say is that EVERY fork is setup to register high speed fork movement AT EXACTLY THE SAME LEVEL!
    No we are not, you are saying that because you didn't know sheiße about high and low speed damping, now you are trying to twist your words around to make it sound like you know something.

  42. #42
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    Quote Originally Posted by Jm.
    No we are not, you are saying that because you didn't know sheiße about high and low speed damping, now you are trying to twist your words around to make it sound like you know something.
    Funny how you keep saying I'm wrong, yet you seem to provide no evidence of what I'm saying as being wrong. How hard is it to understand that not all forks are setup to activate at the same speeds for allowing more fluid to flow?

    Unless you can give us all a set velocity on which all fork manufacturers have agreed to call "high speed", you have no basis on your high speed vs low speed claim.

    Based off the fact that you have offered none of this evidence tells me you are the one seriously confused and that you don't understand that ALL sytems (regardless of how complex) are just a hole (or a hole that varies its own size) that regulates oil pressures. A fork can have a low speed setting that's needed to open up its hole for more fluid flow, yet it will still perform the same at high speeds (high than required to activate high speed ability) and still perform great no matter how much faster the fork moves.

  43. #43
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    Quote Originally Posted by MicroHuck
    Funny how you keep saying I'm wrong, yet you seem to provide no evidence of what I'm saying as being wrong. How hard is it to understand that not all forks are setup to activate at the same speeds for allowing more fluid to flow?

    I didn't say that all forks are setup to activate at the same speeds. You said that.

    Again, high speed vs low speed refers to how fast the fork moves up and down. It seems like this is a very hard thing for you to understand. You should quit now while you are behind.
    Last edited by Jm.; 02-12-2005 at 12:39 PM.

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    Here's a visual aid for people who are confused about what we're talking about here.
    I've shown the difference between HSCV and SSV and a LARGE SSV.

    Basically there's a point in which the fork's compression control is pressurized enough to make it flip open and make its damping hole larger (most high end fork like HSCV actually use multiple small holes, but that's the same as one hole with same volume). It needs to make the damping hole larger in order to allow the fork to move more oil through quickly.

    Marzocchi's HSCV has shims and a spring loaded valve. Both the shims and spring load high speed valve are preset by the factory to a specific zone in the fork's speed where they are forced open by the resulting high fluid pressure, as shown in the graph. As shown in the graph a standard SSV hole will continue to raise oil pressures as the fork speed increases. As shown in the next graph, HSCV and other similar systems will level out the oil pressure and will not allow it to raise quickly with the increase in fork speed.

    Floodgate allows you to tune the point in which the larger hole is activated. Thus it can activate at low speeds, but at the same time be plush on fast hits because the effective oil hole size remains large.
    Attached Images Attached Images

  45. #45
    Uhhhhh...
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    Quote Originally Posted by MicroHuck
    No wonder so many people hate you on this forum. I've never read a single thread where you contributed anything usefull to the topic. I'm not trying to start anything, and for all I know you're a cool guy. Just be a little more on topic and helpfull next time you wish to post.
    And guess how much i care? But i am instituiting a new behavorial program to try and bring the DH/FR forum from the firy pits of hell...

    -TS
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  46. #46
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    Yup.. It's getting a little old now
    It's not a good ride if you don't scare yourself at least once.


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  47. #47
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    Quote Originally Posted by Jm.
    actually there is, compared to how fast the fork moves up and down in a rock garden. I realize this may be beyond some people's comprehension, but it's the reason why a Jr T or dropoff feels quite "plush" while doing a drop or jump, but why they start to feel like crap on the trail when you get to choppy bumps or roots...
    JrT's and DropOffs don't have the HSCV damper, they have the simpler SSVF damper. That's why they suck going thru a rock garden at speed. There's no HSCV for the oil to bleed through. perhaps you need to learn your fork damper types better before using a JrT or DropOff as part of an example.
    I don't post to generate business for myself or make like I'm better than sliced bread

  48. #48
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    Quote Originally Posted by DeeEight
    JrT's and DropOffs don't have the HSCV damper, they have the simpler SSVF damper. That's why they suck going thru a rock garden at speed. There's no HSCV for the oil to bleed through. perhaps you need to learn your fork damper types better before using a JrT or DropOff as part of an example.
    you just said the exact same thing that I did...

  49. #49
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    You guys are far too easily annoyed

    JM does make some good points. I also think he is taken a bit to offensively by the readers. Let it go...

    I have really been trying to find any sort of support to your theory that the floodgate effects damping in the unlocked state. Haven't found anything. I played around with my fork for a few minutes and also found no difference in the unlocked stated turning the floodgate full open-full close. I beleive that the fork must be locked for the floodgate to perform.

    I think I am with AA on the travel being a combination of compressible components and the red spring having very minimal travel. From everything I have read or seen it is really just to take the edge off of the trail chatter when locked.

    WRT high speed and low speed: I am in agreement with JM and think some are being too bull-headed to take in what he is suggesting. Having ridden both SSV and HSCV forks from Marzocchi I think they are in agreement with JM too. High speed movement is most often found at higher velocity over washboard or rocky ground. With a non-hscv fork these sections will really pump up your forearms and wear out your hands. The SSV forks work great for taking big square edge hits like dropping because they spike and prevent the fork from bottoming out. However it is this same spiking that prevents them from achieving high speed damping. **Insert brainfart** I think I just realized what the major issue is. You guys are discussing 2 different items. Fork speed vs speed specific damping. A big hit can be high speed with respect to fork speed. Typically forks that handle big hits are the slower dampers because they spike and slow the fork faster (think ssv). High speed damping will handle everything, but has the tendency to blow through travel or be too harshly sprung on trail chatter. Enter progressive damping and air assited forks. Best of both worlds, high speed damping design and progressive to prevent bottoming.

    Okay, that was fun. Anyone that read all of that thank you.

  50. #50
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    I think we were trying to argue three different things here. Very confusing.

    As shown above, I fully agree that standard SSV type dampers are usually not set up to handle fast hits. It would require a large SSV damper with a light oil that had the same fluid flowing volume as a HSCV damper when it's full open. That would actually perform better at high speeds, but give no lower speed damping. I'm not trying to argue that.

    What I am saying though, is that the HSCV units tend to open their high speed valving on drops, even if they are not considered high speed compared to fast square edged hits. That's all I've been saying. In that regard the fork doesn't care what high velocity you attain, it just cares that you've attained a certain velocity large enough that opens up the secondary oil flowing system, at that point you loose your compression damping pressure that helps prevent the fork from going through too much travel.

    JM seems to think I'm trying to say medium speed hits are super high speed hits. I'm just making the point that after the HSCV system has reached a certain pressure (usually medium to large hits) it opens its secondary system and you loose vital compression pressure. ANYTHING above the pressure point required to open the HSCV is considered high speed regardless of what some people think. This is why I say high speed means different things to different forks.



    The Floodgate on MC most deffinetly does something when not locked out, you just have to ride fast enough or do a drop to notice the difference. The compression knob has such a wide range in adjustment itself that you might not be able to notice the floodgate unless the compression is set to at least half way. You also can't notice these differences just pushing down on the fork.

    With floodgate wide open and compression wide open I can get my stanchion zip tie to get to the top on a 4 ft drop. If I fully close floodgate and leave the compression knob open I get 10mm of travel left. If I then turn the compression knob halfways then I get closer to 20mm left on the same drop. If I turn it much more than that, I get half travel. Angry Asian can confirm this, he talked with people within RockShox for the info on floodgate.




    I now understand what AA was saying about the Motion COntrol unit. Since the spring tube is such a stiff piece it only moves a tiny bit, but moves none the less. The fluid compression rod is skinnier than the fluid reservoir thus giving it a mechanical advantage of multiplying it's force on the spring tube by allowing more fork movement PER amount of spring tube movement. Simply put .5 cm of spring tube movement equals roughly 2cm of fork movement. That makes sense in why the spring tube allows for 20mm of movement without moving 20mm.

  51. #51
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    mleh, MicroHuck most of your points are valid but i still think your trying to twist out of certain points which you were wrong on. Thats all i was pointing out.
    Im certainly not confused and i dont think Jm. is either, i think you misread what we were saying.
    Bit like DeeEight did but no matter.

    Motion Control sounds great, i dont have the chip on my shoulder regarding it that it seems Jm. does but it doesn't make his points any less valid.
    I'd personally like to know how this new bladder techonology on the AM1 works.... sounds intruiging and i rekon it could allow for a similar adjustment as MC but we dont have the knobs to do it cuz its not needed imo, and hence why i went for the AM1..... i dont like fiddling.

    The term bladder technology makes me think of some sort of expandable hole, rather than shims and stacks..... thus the hole would expand as the pressure increases.... perhaps.
    I would really like to know how it works.

    I;ve also learnt loads from recent posts regarding all this stuff..... very interesting reading.

  52. #52
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    Quote Originally Posted by Phip
    I would really like to know how it works.
    The bladder is on the outside of the damping cartridge. I've had it apart and I'd like to know more about how it works too. I guess I could read up on current MX damping technology, as this is what the bladder system is supposed to be the closest to in terms of design and performance.

  53. #53
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    Quote Originally Posted by MicroHuck
    I think we were trying to argue three different things here. Very confusing.

    As shown above, I fully agree that standard SSV type dampers are usually not set up to handle fast hits. It would require a large SSV damper with a light oil that had the same fluid flowing volume as a HSCV damper when it's full open. That would actually perform better at high speeds, but give no lower speed damping. I'm not trying to argue that.

    What I am saying though, is that the HSCV units tend to open their high speed valving on drops, even if they are not considered high speed compared to fast square edged hits. That's all I've been saying. In that regard the fork doesn't care what high velocity you attain, it just cares that you've attained a certain velocity large enough that opens up the secondary oil flowing system, at that point you loose your compression damping pressure that helps prevent the fork from going through too much travel.

    JM seems to think I'm trying to say medium speed hits are super high speed hits. I'm just making the point that after the HSCV system has reached a certain pressure (usually medium to large hits) it opens its secondary system and you loose vital compression pressure. ANYTHING above the pressure point required to open the HSCV is considered high speed regardless of what some people think. This is why I say high speed means different things to different forks.



    The Floodgate on MC most deffinetly does something when not locked out, you just have to ride fast enough or do a drop to notice the difference. The compression knob has such a wide range in adjustment itself that you might not be able to notice the floodgate unless the compression is set to at least half way. You also can't notice these differences just pushing down on the fork.

    With floodgate wide open and compression wide open I can get my stanchion zip tie to get to the top on a 4 ft drop. If I fully close floodgate and leave the compression knob open I get 10mm of travel left. If I then turn the compression knob halfways then I get closer to 20mm left on the same drop. If I turn it much more than that, I get half travel. Angry Asian can confirm this, he talked with people within RockShox for the info on floodgate.




    I now understand what AA was saying about the Motion COntrol unit. Since the spring tube is such a stiff piece it only moves a tiny bit, but moves none the less. The fluid compression rod is skinnier than the fluid reservoir thus giving it a mechanical advantage of multiplying it's force on the spring tube by allowing more fork movement PER amount of spring tube movement. Simply put .5 cm of spring tube movement equals roughly 2cm of fork movement. That makes sense in why the spring tube allows for 20mm of movement without moving 20mm.

    Are you sure that HSCV forks open their high speed valve on drops? I am curious how you know this as it does not make much sense to me.

    I would consider a drop pretty slow compression. I did some fiddling with the 9.8 m/sec2 formula and a 4' (1.33 meter) drop. If I did this right, your initial downward velocity when you hit the ground on a 4' drop to flat (which is a pretty hard hit) is ~.52 m/sec or 18.7 in/sec. Raise it to 6 feet (that is pretty big if you are dropping to a flat) and that speed is .64 m/sec or 23 in/sec. I don't think either of these speeds are very high. Another calculation I did was convert mph into in/sec and got 1mph = 17.6 in/sec, so if you are traveling at even 10 mph that is 176 in/sec.

    OK, here is where I start going into some gross conjecture, but I think it is in the general ballpark: Let's say I hit a 2" root at 15 mph (264 in/sec). Whithout going into trig, I measured 2" off the ground and found that that root will hit my front tire about 6" in front of the very bottom of my tire. This means my fork must compress 2" over an 6" distance. This comes out to the fork compressing at 2/6 x 264 = 88 in/sec. That's 4 times as fast as a 6' drop to flat.

    I realize there are a number of factors I am leaving out here: 1) Depending on the air pressure, the tire can conform to the bump and reduce the amount that the fork compresses, thus making my estimate a little fast. 2) It is not a gradual slope from the point of tire/root contact to the lowest point on the tire. The approach angle at the point of contact is greater than what I use for my calculations, thus making my estimation a little slow. 3) My calculations assume the fork to be perfectly vertical, however I assume that in both the drop and the root impact.

    I would love for others to chime in here as to how to more acurately calculate this and see if I am close. Thanks.

    I think some people confuse a fast hit with a hard hit. When you drop 6', you may only hit the ground at 23 in/sec, but in my case that is about 200 pounds going 23 in/sec that needs to be stopped in the course if 5 inches. Unless I have a super super stiff spring, that will require a good deal of damping. A wheel hitting a root is different. The damper hole that is useful for slowing the drop is way too small for allowing the wheel to roll over easily over the 2" root (thus SSV forks work you on small, high speed chatter) You can afford to have a much bigger damper hole in this high speed situation because all you really need to stop is the wheel, fork lowers and brake that is now traveling at 88 in/sec toward the crown. What are we talking here, 5 or 6 pounds?

    Despite the pissing matches, this has been a good thread, as it has got me really thinking about how this stuff works. Maybe I can finally figure out just how the he11 my 5th coil works. I think that is another thread.

    Kapusta

  54. #54
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    Quote Originally Posted by kapusta

    I would consider a drop pretty slow compression. I did some fiddling with the 9.8 m/sec2 formula and a 4' (1.33 meter) drop. If I did this right, your initial downward velocity when you hit the ground on a 4' drop to flat (which is a pretty hard hit) is ~.52 m/sec or 18.7 in/sec. Raise it to 6 feet (that is pretty big if you are dropping to a flat) and that speed is .64 m/sec or 23 in/sec. I don't think either of these speeds are very high. Another calculation I did was convert mph into in/sec and got 1mph = 17.6 in/sec, so if you are traveling at even 10 mph that is 176 in/sec.
    Props for trying to explain this, but most of us have given up

  55. #55
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    Quote Originally Posted by Jm.
    Props for trying to explain this, but most of us have given up
    Yeah, I guess this horse is pretty dead. I am actually just thinking out loud at this point, but I never really thought about just what the numbers are for shaft velocities in different situations, and now I am curious to know. Any idea where to look?

  56. #56
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    Quote Originally Posted by kapusta
    Yeah, I guess this horse is pretty dead. I am actually just thinking out loud at this point, but I never really thought about just what the numbers are for shaft velocities in different situations, and now I am curious to know. Any idea where to look?
    well, there's equipment that the fork manufacturers can attach to the fork to measure shaft speed and whatnot, but I think your calculations and ideas are spot on. It's simple physics, and as you say for the fork to move and use it's travel efficiantly over a rock or root, it has to do so at a much higher speed shaft than if you "drop" or "jump", which is basically a freefall, 9.8 meters squared and all of that jazz . There's a lot of information out there on dampers though, the motocross world is there to thank for that, and there are some awesome diagrams out there that can visually explain much of this.

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    i thought the red spring thing compresses 2MM to allow oil to flow, and therefore allow the fork to compress. The floodgate knob somehow adjusts the required force needed to uncover whatever the oil flows through. booyakasha.
    pay me

  58. #58
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    Good stuff, Kapusta. Nice to see someone apply a little grey matter around here for a change.
    My video techniques can be found in this thread.

  59. #59
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    It helps a lot to talk about fork damping on a matter of fluid pressure rather than fork speed. The pressure of the fluid flow restriction is directly related the acceration of the fork velocity. It's fluid pressure that determines how the internal mechanisms of fluid control operate.

    While dropping down 4 ft to flat is technically slower (but not slow in comparison to rider movements) than high speed quick hits, there are other factors to be considered. That being, Force and Length of force. A quick hit over a rock has no where near the same duration of impact time a good drop has. It also doesn't have to deal with the downward force of the bike and rider, which is a pretty large force. A drop creates large amounts of fluid pressure, also in part due to the fact that the force helps overcome the compression resistance effects of air and coil springs. Thus the fork will tend to react to the slower speed drop as it would a faster but less forcefull quick hit.

  60. #60
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    Quote Originally Posted by MicroHuck
    It helps a lot to talk about fork damping on a matter of fluid pressure rather than fork speed. The pressure of the fluid flow restriction is directly related the acceration of the fork velocity. It's fluid pressure that determines how the internal mechanisms of fluid control operate.

    While dropping down 4 ft to flat is technically slower (but not slow in comparison to rider movements) than high speed quick hits, there are other factors to be considered. That being, Force and Length of force. A quick hit over a rock has no where near the same duration of impact time a good drop has. It also doesn't have to deal with the downward force of the bike and rider, which is a pretty large force. A drop creates large amounts of fluid pressure, also in part due to the fact that the force helps overcome the compression resistance effects of air and coil springs. Thus the fork will tend to react to the slower speed drop as it would a faster but less forcefull quick hit.
    It is difficult to talk about fluid pressure and not fork speed since fluid pressure is DUE to fork speed. Go back to the fluid and the hole. The resistance to the fluid moving through depends on the velocity of the fluid, NOT the change in velocity. If we are going to get technical, I think momentum would be better to consider than force. Momentum being mass x velocity. Lets use the 6' drop vs. 2" root at 15 mph example. Let's say my bike and I weight 200 lbs and my wheel, fork lowers and brake wieghs 5 lbs. Clearly me and my bike landing a drop have have more momentum than my front wheel being deplected off of a root. I think we are in agreement about that. However, the front wheel has 4 times the velocity. Velocity determines the pressure placed on the valve. True, the quick hit over the rock has nowhere near the duration of a drop (because due to the fact that there is so little mass involved, the shaft is quickly slowed down), but during that brief time the shaft velocity is very high, and so if you do not change the size of the hole, the hit will feel VERY harsh. THIS is the advantage high speed dampers.

    I am not sure why you think acceleration has anything to do with this, but if it did, consider that the 2" root example has a far greater acceleration than the drop. It takes more shaft acceleration to go from 0 - 88 in/sec than 0 - 23 in/sec.

    Kapusta

  61. #61
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    Quote Originally Posted by kapusta
    It is difficult to talk about fluid pressure and not fork speed since fluid pressure is DUE to fork speed. Go back to the fluid and the hole. The resistance to the fluid moving through depends on the velocity of the fluid, NOT the change in velocity. If we are going to get technical, I think momentum would be better to consider than force. Momentum being mass x velocity. Lets use the 6' drop vs. 2" root at 15 mph example. Let's say my bike and I weight 200 lbs and my wheel, fork lowers and brake wieghs 5 lbs. Clearly me and my bike landing a drop have have more momentum than my front wheel being deplected off of a root. I think we are in agreement about that. However, the front wheel has 4 times the velocity. Velocity determines the pressure placed on the valve. True, the quick hit over the rock has nowhere near the duration of a drop (because due to the fact that there is so little mass involved, the shaft is quickly slowed down), but during that brief time the shaft velocity is very high, and so if you do not change the size of the hole, the hit will feel VERY harsh. THIS is the advantage high speed dampers.

    I am not sure why you think acceleration has anything to do with this, but if it did, consider that the 2" root example has a far greater acceleration than the drop. It takes more shaft acceleration to go from 0 - 88 in/sec than 0 - 23 in/sec.

    Kapusta

    Actually, your own graph shows what I am talking about. Fluid pressure as a function of fork speed.

    Kapusta

  62. #62
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    Quote Originally Posted by MicroHuck
    ...there are other factors to be considered. That being, Force and Length of force. A quick hit over a rock has no where near the same duration of impact time a good drop has.
    You guys have been talking about force this whole time. That is not a "new" factor at all. And length of force is a red herring. It has no place in this discussion. The valving sees the fluid pressure as a single instant in time, and decides based solely on that instantaneous pressure which valves to call on to deal with the pressure. It has no memory or forethought which would be necessary if length of force were an issue. Fluids are non-compressible and cannot "develop" and "store" pressure through compression the way gasses can. A longer duration (and slower velocity) impact like a drop causes less pressure against the valving than a quick hit like a square-edge object taken at speed. You need to think about pressure in the same way the valve does: as a discrete moment in time, not as a cumulative force over time.
    My video techniques can be found in this thread.

  63. #63
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    Dude, you're just wrong. High speed compression damping controls bump response. Low speed compression damping controls "feel," i.e., low frequency impulses from pedaling, turning, braking, or other similar loads on the suspension. It has nothing to do with "drops" or "jumps" versus square edge bumps. It has to do with frequency, not the linear speed concept you're obviously stuck on and trying to ponder.

    This isn't just true for mountain bikes - its also true for cars, motocross, and motorcycles. Go find a motorcycle mechanic at a sport bike shop and ask them how they tune the high and low speed compression on their rear shock, and why.

    Or, another mechanical engineer.

  64. #64
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    Close, but not quite. The resistance to the fluid moving through the orifice is caused by viscocity, or resistance to shear deformation - hence the name "viscous damping." This is why higher viscocity fluids will give you more damping than lower viscocity fluids.

    While viscous damping is indeed proportional to velocity, you're thinking incorrectly here. The terms "high speed" and "low speed" damping are referring to the frequency of the impulse on the suspension.

    Low speed compression deals with what we call "feel." Pedaling and turning, or if you're on a motorcycle, twisting the throttle are all low frequency impulses. Their rate of increase and decrease, and thus the duration, is much lower. Rather than plotting the speeds of all these impacts, think about plotting the impulse on your suspension from pedaling versus hitting any sort of bump.

    High speed compression damping deals with bumps, jumps, hucks, drops, and everything else. The impulse is much shorter in duration - it has a higher frequency. While you can sit there and debate what kind of suspension hit is "faster" as you've been doing, all of the things you're discussing are much "higher speed" hits than the previously discussed body forces.

    Your local motorcycle shop can probably explain this in great detail to you, including how it works. Mountain bike and motorcycle dampers are very similar in concept and design.

  65. #65
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    Quote Originally Posted by TXNavy
    Close, but not quite. The resistance to the fluid moving through the orifice is caused by viscocity, or resistance to shear deformation - hence the name "viscous damping." This is why higher viscocity fluids will give you more damping than lower viscocity fluids.

    While viscous damping is indeed proportional to velocity, you're thinking incorrectly here. The terms "high speed" and "low speed" damping are referring to the frequency of the impulse on the suspension.

    Low speed compression deals with what we call "feel." Pedaling and turning, or if you're on a motorcycle, twisting the throttle are all low frequency impulses. Their rate of increase and decrease, and thus the duration, is much lower. Rather than plotting the speeds of all these impacts, think about plotting the impulse on your suspension from pedaling versus hitting any sort of bump.

    High speed compression damping deals with bumps, jumps, hucks, drops, and everything else. The impulse is much shorter in duration - it has a higher frequency. While you can sit there and debate what kind of suspension hit is "faster" as you've been doing, all of the things you're discussing are much "higher speed" hits than the previously discussed body forces.

    Your local motorcycle shop can probably explain this in great detail to you, including how it works. Mountain bike and motorcycle dampers are very similar in concept and design.
    Careful, we've got two different sets of terms here. Marzocchi's HSCV vs SSVF high-speed low-speed is completely different than any type of SPV/Motion Control high-speed low-speed.

    Marzocchi SSV/SSVF - Fork remains active through "slow" hits, including drops/jumps, but fork is not able to handle "fast" hits, such as rock gardens at high speed.

    Marzocchi HSCV - High Spee Compression Valve allows fork to remain active at high speed rocks/roots/etc.

    SPV/Motion Control - Low speed (or low frequency?) effects do not activate the suspension, so pedaling, braking, turning, etc. are cancelled out by the suspension.

    SPV/Motion Control - High speed (or high frequency?) equals any bump, rock, root, etc hit at *any* speed that is enough to overcome the platform valving and activate the fork/rear suspension.

    We now return to your regularly scheduled program.

  66. #66
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    Quote Originally Posted by dante
    Careful, we've got two different sets of terms here. Marzocchi's HSCV vs SSVF high-speed low-speed is completely different than any type of SPV/Motion Control high-speed low-speed.

    Marzocchi SSV/SSVF - Fork remains active through "slow" hits, including drops/jumps, but fork is not able to handle "fast" hits, such as rock gardens at high speed.

    Marzocchi HSCV - High Spee Compression Valve allows fork to remain active at high speed rocks/roots/etc.

    SPV/Motion Control - Low speed (or low frequency?) effects do not activate the suspension, so pedaling, braking, turning, etc. are cancelled out by the suspension.

    SPV/Motion Control - High speed (or high frequency?) equals any bump, rock, root, etc hit at *any* speed that is enough to overcome the platform valving and activate the fork/rear suspension.

    We now return to your regularly scheduled program.

    Good point, and I think you explained what Micro has been trying to say regarding high vs low speed being relative terms.

    Kapusta

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    Quote Originally Posted by Jm.
    Props for trying to explain this, but most of us have given up
    Kapusta, you kick total ass! That exactly the explanation I wanted to give, almost to the T, but I've been way to busy with a tight deadline and a new kid to invest that much time into. Following this thread has been very entertaining....
    "I've come to believe that common sense is not that common" - Matt Timmerman

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    Kapusta:

    I actually did the same calculations as you did (almost exactly the same variables and everything) only moments before getting to your post, and got the same answers: Going over a 3" diameter root compresses your fork about 5x faster than taking a 6 ft drop, assuming a vertical fork and all that. It was funny to stumble across the exact post I was about to write.

    I think what we have here in this post is a general failure to communicate.

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    Quote Originally Posted by dante
    Careful, we've got two different sets of terms here. Marzocchi's HSCV vs SSVF high-speed low-speed is completely different than any type of SPV/Motion Control high-speed low-speed.

    Marzocchi SSV/SSVF - Fork remains active through "slow" hits, including drops/jumps, but fork is not able to handle "fast" hits, such as rock gardens at high speed.

    Marzocchi HSCV - High Spee Compression Valve allows fork to remain active at high speed rocks/roots/etc.

    SPV/Motion Control - Low speed (or low frequency?) effects do not activate the suspension, so pedaling, braking, turning, etc. are cancelled out by the suspension.

    SPV/Motion Control - High speed (or high frequency?) equals any bump, rock, root, etc hit at *any* speed that is enough to overcome the platform valving and activate the fork/rear suspension.

    We now return to your regularly scheduled program.
    The only confusion comes from mixing proprietary terms with proper academic terms I'm using the standard engineering terms from the equation of motion for a second degree system - such as a spring, mass and damper, or suspension to you and me. Its clear that proprietary terms and misunderstanding of physics here are creating issues for people.

    There's two types of damping - that which is proportional to velocity, or viscous damping, and that which is proportional to force, or friction damping. The latter of course is referring to frictional drag in the system, such as from the wiper seals in this case, etc. In all suspension systems applicable here, the damping is of the viscous type.

    What I've tried to correct here is the insistence of examining "slow" and "fast" hits - which you've reiterated again, and added more confusion And think about it - the initial velocity of the fork lower has to be faster on what you're calling a "slow speed hit" - or the suspension wouldn't compress further.

    Rather than trying to illustrate the math, try thinking about dropping a weight on top of a spring. Obviously, the initial velocity of the weight striking the spring will increase with the height from which you drop it, and you can observe for yourself the peak dynamic response of the spring...it will compress more and more as the initial velocity increases. (I'll respond to Kapusta directly about why his model is incorrect, and why the equation of motion is the correct way.)

    Things like SPV and all sorts of different schemes really switch you between "way overdamped" and "damped as you'd like it." High end motorcycle suspensions achieve the same results through different valving schemes, remote reservoirs, etc. While they don't have to deal with pedaling, they do have to deal with low frequency system response from throttle input and braking.

    One Marzocchi scheme gives you only one damping rate - much like a stock Showa shock You're probably fine with an overdamped setup for big hits - but it gives you poor high frequency system response. This is somtimes called "sacking out" the suspension, and often confused with "chatter" (which is actually caused by harmonic response). So another Marzocchi scheme gives you different valving for high frequency response - much like a high end Ohlins shock with remote reservoir and the works. How they interact or are mechanically activated is inane - lots of products for lots of different systems, suspension or otherwise, do just this.

    What's an inertia valve or SPV on low frequency hits other than a very overdamped system? This is why the bike will sag very slowly - but won't respond to higher and higher frequency inputs, like pedaling. The damping is proportional to velocity, so you can move the suspension - just very slowly. Motion control, Marzocchi valving methods...they all aim for the same goal.
    Last edited by TXNavy; 02-14-2005 at 07:37 PM.

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    Kapusta: nice try, but your mathematical model ignores the upward acceleration of your entire bike. You assume the rest of your bike and body stay at a perfect distance away from the ground. This isn't true, even with the best suspension parts

    To look at this problem from an engineering standpoint, you have to start with the equation of motion for the second order system: F=mx"-cx'+kx, where m=mass, x" = acceleration, c = damping constant, and k = the spring constant. The solution to this ODE is well known, and is a sinusoidal oscillation with exponentially decreasing magnitude.

    Let's say that you have an spring, mass and damper at rest. Then you push it down and release it from X1. The motion of the mass up and down is going to look like a sinusoid, right? The velocity will be zero at the top and the bottom, and maximum at the middle, or back at the initial resting point.

    Try pushing the mass down further, to a distance X2, which is further than X1. What you'll notice is that the velocity of the mass at the resting point is greater when the mass is perturbed a greater distance. As the oscillations decrease because of the damper, the velocity in that middle spot gets lower and lower.

    Your fork is the exact same thing. Hits that compress your fork further have higher initial velocities (from the resting point) than ones that compress your fork less. If this example doesn't convince you, try any engineering or physics text book on second order systems, such as a vibrations book. Kudos for at least trying to solve this analytically though!

    As I mentioned previously, the "high and low speed compression" are terms that mislead people this way. It really refers to the high and low speed frequency response of the system, not velocity of any single part. The different valving schemes used by manufacturers are really methods of changing viscous damping rates to achieve different frequency response characteristics. High damping for low speed compression - low damping for high speed compression.
    Last edited by TXNavy; 02-14-2005 at 07:39 PM.

  71. #71
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    Quote Originally Posted by TXNavy
    Kapusta: nice try, but your mathematical model ignores the upward acceleration of your entire bike. You assume the rest of your bike and body stay at a perfect distance away from the ground. This isn't true, even with the best suspension parts

    To look at this problem from an engineering standpoint, you have to start with the equation of motion for the second order system: F=mx"-cx'+kx, where m=mass, x" = acceleration, c = damping constant, and k = the spring constant. The solution to this ODE is well known, and is a sinusoidal oscillation with exponentially decreasing magnitude.

    Let's say that you have an spring, mass and damper at rest. Then you push it down and release it from X1. The motion of the mass up and down is going to look like a sinusoid, right? The velocity will be zero at the top and the bottom, and maximum at the middle, or back at the initial resting point.

    Try pushing the mass down further, to a distance X2, which is further than X1. What you'll notice is that the velocity of the mass at the resting point is greater when the mass is perturbed a greater distance. As the oscillations decrease because of the damper, the velocity in that middle spot gets lower and lower.

    Your fork is the exact same thing. Hits that compress your fork further have higher initial velocities (from the resting point) than ones that compress your fork less. If this example doesn't convince you, try any engineering or physics text book on second order systems, such as a vibrations book. Kudos for at least trying to solve this analytically though!

    As I mentioned previously, the "high and low speed compression" are terms that mislead people this way. It really refers to the high and low speed frequency response of the system, not velocity of any single part. The different valving schemes used by manufacturers are really methods of changing viscous damping rates to achieve different frequency response characteristics. High damping for low speed compression - low damping for high speed compression.
    I am responding to this post as well as the one farther down. I am enjoying this thread as it has me thinking alot about something I had not put a lot of thought into before. Hey, I could be dead wrong here, but this is where my logic is taking me.....

    I am standing by my model for now. I basically understand the concept of a second order formula. It does a perfect job at describing the change in position over time as a damped spring goes through it's stroke and back again, but I don't think that is what is needed here. First of all, if a bike shock goes through more than one sine wave cycle from a single hit, then there is something wrong with the damper.

    When you say that...

    "Hits that compress your fork further have higher initial velocities (from the resting point) than ones that compress your fork less"

    and use the example.....(in the other post)

    "try thinking about dropping a weight on top of a spring. Obviously, the initial velocity of the weight striking the spring will increase with the height from which you drop it, and you can observe for yourself the peak dynamic response of the spring...it will compress more and more as the initial velocity increases"

    ....you are missing the difference between a drop and hitting a 2" root at 15 mph. True, given a constant mass, the higher you drop it from, the higher the initial velocity and the farther it will compress the spring. And it is also true that the farther you drop on a bike, the faster the initial shaft velocity when you hit the ground and the farther the shock compresses. OK, we are in agreement on that. The second order formula backs this up, and it is intuitive as well.

    Hitting a root is different, and here is why: When the wheel first hits the root, the fork is compressed at a very high rate of speed. True, my model did not take into account the fact that when I hit the bump, me and the bike were deflected up, therefore reducing the shaft speed. I'll take that into account now. When I hit that root, the initial shaft velocity is, say, 88 in/sec (I'm sticking with that number for now). To the spring, this "looks" like the weight of me and my bike hitting the ground at 88 in/sec, and compressing it at this rate (after all, if my bike and I weighed nothing, the shock would not compress). Over the 2" of travel to get over the root, the spring and damper have slowed the shaft. It did this by pushing the bike up. This is where the acceleration you were talking about comes from (as you probably already know) and this is, I believe, consistent with the second order formula. The spring cannot change the velocity of the earth (practically speaking) but the rate of compression is slowed by accelerating the bike upwards. I do not see how this would be different than hitting the ground from a drop. As the spring slows it's rate of compression, me and my bike are accelerated upwards, slowing my fall. Going back to the example of dropping a weight on a spring, the spring is accelerating the mass upwards, the farther the spring is compressed, the greater the acceleration. Sorry, I diverge....

    OK, so far I think we should still be in agreement. Here is where it changes: Once the tire clears the 2" root, all of the mass of me and my bike go away! The second order formula assumes a constant mass. The mass was constant as the fork compressed over the root, but now it is suddenly out of the picture. Now all you have is the mass of a wheel, fork lowers, and the front brake, so if you are going to use the second order formula, you now need to plug in a much smaller mass. Actually, I am not sure exactly what to plug in for mass since neither side of the spring is against something imobile like the earth, but it is certainly much less than it was.

    This is why you can have a higher speed (and I mean velocity) hit that does not compress the spring as much as a lower velocity hit. The masses are not the same once the bump is cleared.

    So far as what high and low speed refer to, it is clear from this thread that it means a lot of things to a lot of people. I don't think it is correct to say it is only about frequency. That does not make sense to me or jive with my understanding of a high speed damper, such as HSCV. The valve opens when the fluid reaches a certain velocity. One single, fast hit will open it. How is this frequency dependent? When the shaft or fluid reach a certain velocity, the hole gets bigger.

    Could you clarify one point you made? you said......

    "Try pushing the mass down further, to a distance X2, which is further than X1. What you'll notice is that the velocity of the mass at the resting point is greater when the mass is perturbed a greater distance"

    Isn't the velocity at the resting point zero? I assume the resting point is at the very top and bottom? Or does "resting " refer to the middle of the sine wave where the net acceleration is zero?

    I am really not familiar with motorcycle or car damping systems beyond the basic theory, but I think I do understand the concepts fairly well with respect to bikes.

    Good stuff!!!

    Kapusta

  72. #72
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    Quote Originally Posted by TXNavy
    The only confusion comes from mixing proprietary terms with proper academic terms I'm using the standard engineering terms from the equation of motion for a second degree system - such as a spring, mass and damper, or suspension to you and me. Its clear that proprietary terms and misunderstanding of physics here are creating issues for people.

    There's two types of damping - that which is proportional to velocity, or viscous damping, and that which is proportional to force, or friction damping. The latter of course is referring to frictional drag in the system, such as from the wiper seals in this case, etc. In all suspension systems applicable here, the damping is of the viscous type.

    What I've tried to correct here is the insistence of examining "slow" and "fast" hits - which you've reiterated again, and added more confusion And think about it - the initial velocity of the fork lower has to be faster on what you're calling a "slow speed hit" - or the suspension wouldn't compress further.

    Rather than trying to illustrate the math, try thinking about dropping a weight on top of a spring. Obviously, the initial velocity of the weight striking the spring will increase with the height from which you drop it, and you can observe for yourself the peak dynamic response of the spring...it will compress more and more as the initial velocity increases. (I'll respond to Kapusta directly about why his model is incorrect, and why the equation of motion is the correct way.)

    Things like SPV and all sorts of different schemes really switch you between "way overdamped" and "damped as you'd like it." High end motorcycle suspensions achieve the same results through different valving schemes, remote reservoirs, etc. While they don't have to deal with pedaling, they do have to deal with low frequency system response from throttle input and braking.

    One Marzocchi scheme gives you only one damping rate - much like a stock Showa shock You're probably fine with an overdamped setup for big hits - but it gives you poor high frequency system response. This is somtimes called "sacking out" the suspension, and often confused with "chatter" (which is actually caused by harmonic response). So another Marzocchi scheme gives you different valving for high frequency response - much like a high end Ohlins shock with remote reservoir and the works. How they interact or are mechanically activated is inane - lots of products for lots of different systems, suspension or otherwise, do just this.

    What's an inertia valve or SPV on low frequency hits other than a very overdamped system? This is why the bike will sag very slowly - but won't respond to higher and higher frequency inputs, like pedaling. The damping is proportional to velocity, so you can move the suspension - just very slowly. Motion control, Marzocchi valving methods...they all aim for the same goal.
    I reasponded to this up above

    Kapusta

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    Quote Originally Posted by kapusta
    I am standing by my model for now. I basically understand the concept of a second order formula. It does a perfect job at describing the change in position over time as a damped spring goes through it's stroke and back again, but I don't think that is what is needed here.
    Well, okay, but I don't see why. This is the basic equation that describes the motion you're trying to explain. This applies to everything from suspensions to the springs that we place under heavy machinery in factories or on ships (they reduce the impulse transmitted to the deck - just like your suspension).

    Here's a nifty animation that shows the response of a single degree of freedom (DOF) spring-mass system to base excitation (the earth moving up, as you said), which is really what we're discussing.

    http://www.kettering.edu/~drussell/D...aseMotion.html

    One caveat, this graphic is showing response to a harmonic response, rather than a transient impulse!

    First of all, if a bike shock goes through more than one sine wave cycle from a single hit, then there is something wrong with the damper.
    Well yeah but that's beside the point, as I'm only trying to explain harmonic motion If the suspension is critically or overdamped, it won't oscillate. But some are underdamped, either by poor (cheap) design, or other desired effects. I'm not necessarily talking only about mountain bikes, either. It depends on what characteristics the engineer wants out of the system. Sometimes you want certain spring rates, but to compensate for that you have to use underdamping...it all depends.

    you are missing the difference between a drop and hitting a 2" root at 15 mph. True, given a constant mass, the higher you drop it from, the higher the initial velocity and the farther it will compress the spring. And it is also true that the farther you drop on a bike, the faster the initial shaft velocity when you hit the ground and the farther the shock compresses. OK, we are in agreement on that. The second order formula backs this up, and it is intuitive as well.
    So I'm not missing the difference. Why do you change your mind below if the basic differential equation verifies the answer?

    Hitting a root is different, and here is why: When the wheel first hits the root, the fork is compressed at a very high rate of speed. True, my model did not take into account the fact that when I hit the bump, me and the bike were deflected up, therefore reducing the shaft speed. I'll take that into account now. When I hit that root, the initial shaft velocity is, say, 88 in/sec (I'm sticking with that number for now). To the spring, this "looks" like the weight of me and my bike hitting the ground at 88 in/sec, and compressing it at this rate (after all, if my bike and I weighed nothing, the shock would not compress).
    Aaahhhh not exactly. You're thinking of the spring really in the static sense rather than the dynamic, transient response sense.

    Over the 2" of travel to get over the root,
    Your suspension doesn't compress two inches when you go over a two inch root, and your speed analogy is kind of the other way around...but this'll take some explaining. (That professor's webpage has more harmonic response stuff on it.)

    Let's think about this another way. Think about riding over the root at different speeds. Is there a low speed where it won't compress much...an intermediate speed where it'll compress a lot...and then faster speeds than that where it'll compress a lot, but your bike is still forced upwards, with higher and higher force proportional to speed?

    The answer to this question of course has to do with system response above or below the natural frequency of the spring-mass system due to base excitation. (As one of the ship shock professors here always says...its the base excitation that always gets you!) You simply cannot escape the equation of motion on this one

    In the first case at low speed, you're below the natural frequency. The system responds statically, i.e., as if it were nearly solid. Imagine pushing your bike up slowly by hand by the fork lower. In the second case, you're at the natural frequency. In the third case, you're well above the natural frequency and responding statically again during the transient response. But, the response is 180 degrees out of phase, so the system can't respond as quickly.

    This is why this is really about frequency response rather than "speed" of the fork lower. I know, its twisted and I'm not good at explaining these things.

    the spring and damper have slowed the shaft. It did this by pushing the bike up. This is where the acceleration you were talking about comes from (as you probably already know) and this is, I believe, consistent with the second order formula.
    To use the ODE you have to fix your coordinate system, which is hanging you up. If you fix it to earth, you still have to reference the spring to the bike back to the earth - which basically translates into "less compression = lower initial velocity," no matter how you set up your equations.

    The spring cannot change the velocity of the earth (practically speaking) but the rate of compression is slowed by accelerating the bike upwards. I do not see how this would be different than hitting the ground from a drop.
    I think the best I can say is think "base excitation."

    OK, so far I think we should still be in agreement. Here is where it changes: Once the tire clears the 2" root, all of the mass of me and my bike go away!
    Uhhhh...no.

    The second order formula assumes a constant mass. The mass was constant as the fork compressed over the root, but now it is suddenly out of the picture. Now all you have is the mass of a wheel, fork lowers, and the front brake, so if you are going to use the second order formula, you now need to plug in a much smaller mass.
    Okay, a qualified "no." You're on a tangent

    So far as what high and low speed refer to, it is clear from this thread that it means a lot of things to a lot of people. I don't think it is correct to say it is only about frequency.
    But it is. Seriously - ask an engineer other than myself, or better yet, go to the local motorcycle shop and ask them about tuning the high and low speed compression circuits on their bikes.

    They may not understand the frequency response mathematics, but they can verify what the two circuits do, at least in the layman's sense. Low speed compression affects low frequency inputs - what we call "feel." High speed compression is bump sensitivity.

    That does not make sense to me or jive with my understanding of a high speed damper, such as HSCV. The valve opens when the fluid reaches a certain velocity. One single, fast hit will open it. How is this frequency dependent? When the shaft or fluid reach a certain velocity, the hole gets bigger.
    Well, let's think about it for a minute. What's the relationship between damping and the natural frequency of the spring/mass/damper system? Increasing damping lowers the natural frequency, right? And vice versa, decreasing damping will raise it, right?

    Different valving schemes open or close orifices to increase and decrease the viscous damping ratio. In the system you're describing, the damping ratio is reduced so the system's natural damped frequency is raised while encountering high frequency inputs. The system's response rate is likewise increased, so its free to move over the little bumps.

    Remember, the response of a spring-mass-damper system to an impulse transient input is a harmonic response at the naturally damped frequency, right? So if I kept a really low frequency response rate, small bumps would jar me upward as the system doesn't have the response time we'd like. So instead, we change the frequency to something higher when we're in the bumps. The fork reacts quicker in terms of frequency.

    The fork lower will go up at exactly the same speed regardless of what the rest of you does, right? So what makes the difference in how fast the rest of you goes up and down? The frequency response of the system!

    Isn't the velocity at the resting point zero? I assume the resting point is at the very top and bottom? Or does "resting " refer to the middle of the sine wave where the net acceleration is zero?
    The resting point is always the equilibrium point, where the mass will returrn to as time goes to infinity. In the animation, its the zero line. True harmonic motion always oscillates equally about the resting point.

    Non-linear or "progressive" springs don't have harmonic motion so they're a little different. But in almost all the cases you'll ever come across, these are the relationships you're dealing with. (Unless you upgrade your sportbike to very-progressive springs from Hyperpro like I did.)

    I am really not familiar with motorcycle or car damping systems beyond the basic theory, but I think I do understand the concepts fairly well with respect to bikes.
    Well, the neat thing is that its all the same. Not only does it apply to vehicle suspensions, it also applies to things like "how to damp the motion of the clothes dryer on the submarine so less than 20% of its impulse force is transmitted to the deck as noise." You also don't really need to know differential equations to "get it." I don't know for sure, but I'd bet there's plenty of people in mountain biking who are really designing these things as much by feel and intution as by engineering degree.

    Good stuff!!!
    I agree!

    BTW, the original poster's comments about RS's motion control were indeed, uh, spotty at best...but he gets ten points for enthusiasm...

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    "Hits that compress your fork further have higher initial velocities (from the resting point) than ones that compress your fork less."

    as said before, not always. you have to take duration into account. The duration of a hit from a 2" root is very low, when landing a drop your mass will carry on pushing down on the fork until the spring and damping slow it down to a halt and then return itself to the correct length.
    Drops and roots have to be explained in a different way.

    I dont understand half of the terminology going on here but have a basic grasp (only a 1st year Engineer) but im more inclined to agree with Kapusta. SSV/SSVF and HSCV really are quite different to MC/SPV but that still doesn;t change the fact that a drop really is low speed when compared to roots and rocks at 15mph. This is what we were saying and Microhuck was just trying to dig his way out of being wrong by then going on about how different systems have different threshholds. Ofcourse thats true but we are being general when talking about TPC+ and HSCV and how they deal with the 2. SSV handle drops fine because its slow speed, it has a longer time to get the fluid through the hole and thus a high speed valve is not needed, a 2" root at 15mph does not give SSV enough time to get the fluid through and thus why they spike on such things.
    The distance the spring compresses does not only rely on initial velocity and mass, that is only in basic principles where mass is constant. Once over a small root the mass is removed and thus the spring is able to extend again.

    Thats how i see it and it makes perfect sense.

    Motocycle shocks are set up differently. They use the same principles but in practical situations are used differently. Your not gonna do a 6' drop on a road bike........ you want to compare more to moto-cross bikes than road bikes.

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    Yes.

    Quote Originally Posted by TheSherpa
    Doesn't this guy annoy the phuck outta you? He thinks he knows everything, yet lacks some very basic knowledge.

    -TS
    Yes. I also don't understand his need to be so insulting all the time.

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    Quote Originally Posted by kapusta
    It is difficult to talk about fluid pressure and not fork speed since fluid pressure is DUE to fork speed. Go back to the fluid and the hole. The resistance to the fluid moving through depends on the velocity of the fluid, NOT the change in velocity.
    Bzzzzt Wrong...

    These are pure mechanical forks and dampers. There's no way to calculate the velocity of the fluid moving to determine the opening of a valve... the pressure though, that's something that's possible within the confines of the valve body space. This is why they use shim stacks and springs inside the damper. They control the pressure resistance of the valving. The only bicycle shocks to ever accurately take velocity of hits into account were the Noleen smart shocks, which also went thru a 9V battery in about 8 hours of operation, and used the electronics to vary the compression damping automatically depending on the type of impacts being applied to the suspension. .


    If we are going to get technical, I think momentum would be better to consider than force. Momentum being mass x velocity. Lets use the 6' drop vs. 2" root at 15 mph example. Let's say my bike and I weight 200 lbs and my wheel, fork lowers and brake wieghs 5 lbs. Clearly me and my bike landing a drop have have more momentum than my front wheel being deplected off of a root. I think we are in agreement about that. However, the front wheel has 4 times the velocity. Velocity determines the pressure placed on the valve. True, the quick hit over the rock has nowhere near the duration of a drop (because due to the fact that there is so little mass involved, the shaft is quickly slowed down), but during that brief time the shaft velocity is very high, and so if you do not change the size of the hole, the hit will feel VERY harsh. THIS is the advantage high speed dampers.
    yes but again, its fluid pressure that is important, not velocity. Any as the oil forces its way thru the damper, the pressure changes. Small shaft movements don't produce the same sort of pressure spikes than large movements do. You're also limiting your math to vertical velocity, which isn't appropriate since the dampers usually aren't absorbing impacts in direct line with the motion of the bike. Root hits come from head on for example and forward velocity plays a part in the math, which you seem to be forgetting.
    I don't post to generate business for myself or make like I'm better than sliced bread

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    but surely a fast movement will create a higher pressure because as the fork compresses (which it tries to do by the 2" or so) then thats 2" of travel and however much oil that has to be move near instantaneously thus having the need for an extra large valve for the oil to pass through.
    Though a big hit will move more oil in total, this is spread over a much longer period of time thus reducing the pressure and making the low speed valve able to reduce the pressure enough by allowing the oil through meaning the pressure doesn;t build enough for the high speed valve to be opened.....

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    The problem with trying to calculate fast and slower hits is that we don't live in a perfect world where forces transfer instantly. On a drop you will get the full force of the bike AND the human body coming down on the fork, this is considered a longer duration impact.

    When I say longer duration, I'm not really talking about fork movement. What I'm refering to is the amount of time allowed for the full wieght to transfer into the fork. On a really quick hit on a rock the human body will take a good amount of the force regardless of how plush your fork is. There are also the other factors such as the tires, rear suspension, and the rotation of the bike that "BUFFER" the impact. A drop bypasses ALL of those buffer zones and provides for an quick force on the fork.

    I will admit I'm not very good at making my point clear even though I type a lot. Besides the issue of the compression spring tube, most of what I've said so far has been spot on, especially in regards to setting up Motion Control. You guys keep saying I'm trying to dig out of a hole, yet I've been saying the same thing the whole time. Someone else said "a drop is higher speed than small bump", not me, I would never argue that. What I said was "both a drop and fast bump are considered high speed." That's where having different damping systems comes into play, because each system is designed with different thresholds. One fork may open its secondary system on a 6 inch drop and EVERYTHING above that point in speed is considered high speed for all the fork cares for! When that fork's secondary system opens up and gives twice as much damping hole volume it is ready for any speed of hit. A large ported SSV damper works better than anything else at high speeds for the same reason, it's already large enough to flow enough fluid at high speeds (just happens that they don't make SSV large enough for that). Thus the level of oil pressure at which the higher speed system operates defines what is high speed above that point, thus each fork in itself defines high and low speed, not someones generalization of fork velocities.

    You can talk fork speed all you want, but in the end it's oil pressure that determines the internal function of a fork. Just because a fast hit creates a lot of quick pressure doesn't mean that slower hits with more force don't activate the same mechanisms. I don't really see any way to argue that....?....

    Why would so many people with HSCV complain of no compression damping on drops? That alone tells us HSCV activates on drops, so all the mathematical mumbo jumbo can be thrown out the window on that one. Let's see, fork feels controlled on rider movements and slow movements (fork is doing it's job at maintaining low speed compression), rider does drop and loses fluid damping resistance (sign of HSCV valve doing its thing). What else is there to understand? For all the fork cares, the drop is a high speed hit (high pressure hit), it's already opened into its mode of the most fluid movement allowed by the system, which also accomodates quick pressure hits too.
    Last edited by MicroHuck; 02-15-2005 at 04:44 PM.

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    Quote Originally Posted by Phip
    as said before, not always. you have to take duration into account. The duration of a hit from a 2" root is very low, when landing a drop your mass will carry on pushing down on the fork until the spring and damping slow it down to a halt and then return itself to the correct length.
    Drops and roots have to be explained in a different way.
    Don't think "duration." Think "period." Low frequency impulses are those which have a long period - such as pedaling inputs. High frequency impulses are those which have short duration, such as any hit.

    I dont understand half of the terminology going on here but have a basic grasp (only a 1st year Engineer) but im more inclined to agree with Kapusta.
    I'm six months from completing my masters in MechE, so its your call. Find a professor at your school who teaches vibrations for MechE, or any math professor about ODE's and ask them about how to approach this problem. Its really something that almost everyone looks at in a vibrations course.

    SSV/SSVF and HSCV really are quite different to MC/SPV but that still doesn;t change the fact that a drop really is low speed when compared to roots and rocks at 15mph.
    It is? Because you think its slow since you're compressing your fork so much more, or because of mathematical reasoning? Let's look at it again.

    The equation of motion is really simple and about balancing forces: momentum, damping, and spring force.

    Put your theoretical mass back on the spring. I want you to hit it hard, then soft. The hard hit is your drop, and the soft hit is your root.

    Does the period or "duration" of the frequency response change?

    Add a damper. How does this change the response of the system to perturbation?

    It may be just me, but I'm pretty sure that the frequency won't change regardless of how fast you hit it

    This is what we were saying and Microhuck was just trying to dig his way out of being wrong by then going on about how different systems have different threshholds.
    Well, you were right to hit him on some points. But that's also where you guys diverged from science on the finer points. Yes, he said some wrong things. But really, you can't just fudge acceleration and velocity data this way.

    There's two ways to solve for the initial acceleration and velocity of the system. One uses accelerometers. I doubt the MechE lab is going to let me take a few tonight, and I'd hate to ride around with that signal processor on my back anyway.

    The other way is to look at the initial perturbation and solve for the equation of motion. That's how engineers do it.

    a 2" root at 15mph does not give SSV enough time to get the fluid through and thus why they spike on such things.
    Well, the rest of us engineers are convinced that in a noncompressible fluid in a control volume, pressure is transmitted instantaneously to all parts of the fluid.

    Seriously - the damping is too high and the frequency response is too low. When you land on a drop or a big hit, you don't care because its "good" to have a lower frequency response. You want the energy dissipated over a longer duration. Over small hits, it sacks out your suspension.

    The valving in SSV may not open "enough" to make a difference, and the frequency response is still too low. What I would suspect is that its really just overdamped in either case, and the frequency response bears this out.

    The distance the spring compresses does not only rely on initial velocity and mass, that is only in basic principles where mass is constant. Once over a small root the mass is removed and thus the spring is able to extend again.
    No. This is a misunderstanding on your part, and if you don't believe me now, you will when you take some more classes on it. If you go over a root that fast, to where you're no longer touching the ground, then you've exceeded the natural frequency of your suspension system. What's the frequency response of a system above its natural damped frequency?

    If you push your mass and spring down really fast and withdraw your hand, faster than the natural frequency, then obviously your hand is going to leave contact with the mass. Its frequency response is "slower" than the impulse from your hand. It'll be leave your hand compressed and possibly compress more - because its now 180 degrees out of phase with your input.

    This is a design point for all suspensions, not just mountain bikes. Spring and damper rates are tuned for different kinds of bumps this way. Think about it...what do you do on a fork if its not able to handle rough washboard roads? You decrease your rebound damping - to raise the frequency response of the system! People think of it as "making it more bouncy" but what you're really doing is tuning the frequency response.

    This is why in my previous post I went over three different speed scenarios for going over the root. One below the natural frequency of you and your bike, one at it, and one well above it. What you're describing is well above it.

    And we haven't even gotten to square edged bumps, which are really just step inputs to the system, right?

    Thats how i see it and it makes perfect sense.
    Well, you should try to apply the equations of motion to the problem and reanalyze. There's only a few things like turbulent fluid flow that are truly difficult to explain from first principles.

    Motocycle shocks are set up differently. They use the same principles but in practical situations are used differently. Your not gonna do a 6' drop on a road bike........ you want to compare more to moto-cross bikes than road bikes.
    Well, no, but the exact same principles are used on motorcycles, cars, trucks, giant Dresser earth movers, you name it. I tune my motorcycle suspensions based on guess what? A couple of my friends did thesis work on motocross suspension based on - guess what? Another guy did thesis work based on the frequency response of a HUMVEE suspension over different bumps (frequency inputs) and how it affected electronic gear in the vehicle.

    Frequency response to low speed and high speed input Is it sacked out going over rough surfaces? Is it too bouncy? Is it underdamped, critically damped, or overdamped? Just like your school, I could probably take your fork, put it on our shaker table, hook up accelerometers, and derive everything we need to know about it - including its frequency response going over different types of inputs.

    Think about it
    Last edited by TXNavy; 02-15-2005 at 05:19 PM.

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    Boy! This thread was meant to help people understand how to set up their fork! All I think has happend is more confusion. LOL

    We really need someone who makes fork damping systems to tell us all to shut up and end it here. Seems like every person is argueing a different thing.

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    Well at least it works.

    I bought a used 04 firefly and had a small spill due to the poor/different damping system. Four years of TPC+ had spoiled me I guess.

    My question is, will the Pike I ordered from the LBS work as well as my old X-Vert? I know it has a beefy chassis and will track better.

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    I've thought of an even better example.

    Put the spring and the mass in your hand. Kind of like a bike and fork on the ground

    When you move your hand up very slowly, below the natural damped frequency, the spring barely compresses, right? What we say here is that its responding nearly statically. The mass moves in phase with the input.

    Now, when you move your hand up and down at the natural damped frequency, what happens? The mass is 90 degrees out of phase with the input. To draw the parallel on your mountain bike, this is the "quickest" you can get over a bump with your suspension staying firmly on the ground.

    Now when you move your hand up and down faster than the natural damped frequency, what happens? The spring starts leaving your hand, right? If the spring were to remain attached to your hand, you would see the mass moving up and down opposed to the direction of your hand - its 180 degrees out of phase. This is what happens when your suspension is over-damped for the frequency of input, and is "sacked out," and what you're trying to describe with your wheel leaving the ground temporarily. You feel it at your handlebars as the fork's inability to "move fast enough" to compensate for the little bumps. It has nothing to do with the compression speed - it has to do with the frequency response.

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    TXNavey, you are obviously very well versed in the concepts you are describing. However, it seems to me that you have a great hammer, and everything is looking like a nail to you.

    First I want to make sure that we stick to the two points that I believe we are (in a gentleman's fashion, hopefully) debating:

    1) You stated ... "the initial velocity of the fork lower has to be faster on what you're calling a "slow speed hit" - or the suspension wouldn't compress further".... and reiterated this point in another post. I dissagree and I am attempting to explain how you can have a hit (root) create a greater initial velocity and yet have the suspension compress less than on a slower hit (drop)

    2) Speed sensitive dampers respond to shaft speed, not vibration frequency.

    You have a great understanding of harmonic resonance, frequency response, and such. (I used these concepts alot as a sound technician back in the day, and this is starting to bring alot of it back to me) But I think you are mis applying them here, or at least to the point being debated. The harmonic resonance of a fork is FAR slower than the high speed hit we are discussing. Going to the link you gave me makes me realize that you are looking at these bumps as a steady, consistent, repeating motion. If that were the case then these concepts (Harmonic resonance, frequency response, out of phase) would be pretty much all we need. I can see that they are extremely relavent in street cars and street bikes, as you do encounter consistent, repeating motion that could wreak havok if not dealt with. But even with street cars and motorcycles there are other factors to be dealt with. Forces where it is the amplitude, not the frequecy that is the issue (a 6" deep pothole) This is especially true of mountain bikes. You are going to need something besides these few formulas to describe what happens as you plow over randomly distributed roots. Or a single root.

    Of course the response frequency has SOMETHING to do with the behavior of the fork. I think your example of hitting a root at different speeds was acurate to a certain extent. There are certain speeds at which an improperly damped fork will actually magnify the effects of the root. I think many of us have experienced this. However, in the example of hitting a root at high speed, we are talking about a properly damped fork at a speed far beyond the resonant frequency.

    The second order model does fit into this as well, and you are correct that you cannot escape it. However, I do not think you are applying it properly. I am speaking of your assertion that initial velocity is the sole determination of how far the shock compresses. I don't think you followed my example. Your model of a mass dropping on a damped spring DOES model a drop fairly well. It does NOT model hitting a root at speed very well. I don't see how you can get around the initial shaft velocity being very high when you hit a 2" root at 15 mph. Show me where my math was significantly off.

    (D8 mentioned something about direction of force, but the shock is going to respond to the force along IT'S line of shaft movement. As I said, I did assume the shaft to be straight up and down, but I think my number are at least in the ball park. D8, If you have significantly different numbers, show how you get them)

    You seem to think that the bike accelerating upwards changes this. Fine, it does accelerate, but it accelerates from REST. At the first small moment after the impact, the wheel is travelling very fast and the bike is just beginning to accelerate and is going very slow. The difference in these speeds is the shaft velocity and it is higher that that seen in a drop. Acceleration is not an instantanious incease in velocity, is a gradual one. This is especially true if it is due to being pushed by a spring. The front wheel accelerates upwards at a FAR greater rate than the bike does (the tire is a MUCH stiffer spring that the shock), and the higher the tire pressure the faster the acceleration. OK, so if this is the case (the shaft velocity is greater than in a drop), why doesn't the shock compress more from this high initial velocity than the lower velocity seen in the drop? At first glance the second order formula seems to say otherwise, and I think this is what you are stuck on. What I think you are missing is that once the root is cleared the variable for mass is greatly reduced, and you need to re-work the formula using this new mass. What I believe you will get is a motion that is slowed down much more quickly and does not reach the same amplitude. Clearly the forces present as the wheel was being pushed upwards for the first two inches are very different now. Now all you have is a 5 or 6 pound mass traveling upwards to slow down. (iI'll get to your spring in hand example below which is, I believe, completely consistent with what I am saying here)

    I THINK you may be working backwards on this. I THINK what you are doing is looking at that fact that a shock does not compress as far on a high speed hit on a root as for a drop, and determining that the initial velocity MUST therefore be less. You use the second order formula to back this up, but you are not taking into account that a key variable changes part way through the scenario: The mass that the spring is dealing with. I think that if you re-worked the equation with this, you would find that you CAN in fact have a higher initial velocity and yet have a shorter total compression.

    I just read your spring in the hand example. It makes perfect sense, but I am at a loss as to what your point is. I am saying that a root hit at high speed causes a very high initial shaft velocity, and yet it does not cause the shock to compress as much as the lower speed drop. This was the entire point of my last post. You just described WHY such a fast hit causes my bike to buck and the wheel to not return to the ground fast enough. Great, a clear and concise aplication of resonance theory, but what is your point? You just decribed what I am saying happens in great detail.

    Notice that you needed a DIFFERENT example for hitting a root than for landing a drop? Of course all the rules of resonance, second order equations, and frequency response apply to both, but the practical results are different. It's apples and oranges.

    Let's look at the spring-in-hand example. Had you lifted your hand and kept lifting it at a steady rate, then motion of the spring with the mass on top would very much resemble the motion caused by a drop, and would be neatly explained as a second order motion. But that is not what you are doing. You are quickly lifting it AND THEN PULLING YOUR HAND BACK DOWN. You are therefore NOT going to compress the spring as much. This a perfect illustration of what I am talking about.

    Here is another problem the second order equation runs into in the real world when you use it to model motion. The damping on forks is nothing close to constant. Rebound and compression are often set at vastly different levels. Comression damping may vary with position (position sensitive damping) or shaft speed (speed sensitive damping), Well, OK the shaft speed is still being debated here.

    As I said, I agree that the second order formula will always work, but it is far more complicated than plugging in one set of numbers and leaving it at that. Real world factors mean that these variables (mass and damping) are constanly changing, and in this case comparing a drop to a root is apples and oranges.


    As to the question of high speed dampers responding to frequency: There seems to be another debate going as to on whether they respond to pressure or velocity. My veiw is that the two are linked, and one is the function of the other. I am still scratching my head as to which is a function of which, but they do vary together, though not proportionally. Whichever one the high speed valve responds to, both can vary independent of frequency. Think of a fork moving up and down 1 inch 5 times per second. The frequency is 5Hz. Now, move fork up and down 5 inch 5 times per second. Same frequency, 5Hz, but the oil pressure, or velocity, (whichever you claim opens the valve) is WAY higher.

    Kapusta

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    Quote Originally Posted by kapusta
    TXNavey, you are obviously very well versed in the concepts you are describing. However, it seems to me that you have a great hammer, and everything is looking like a nail to you.
    Well, it is a good hammer. That's why its called first principles, and everything else is based on it.

    2You have a great understanding of harmonic resonance, frequency response, and such. (I used these concepts alot as a sound technician back in the day, and this is starting to bring alot of it back to me)
    I should have a great understanding of it. I'm a mechanical engineering graduate student who analyzes systems like this on a regular basis.

    But I think you are mis applying them here, or at least to the point being debated. The harmonic resonance of a fork is FAR slower than the high speed hit we are discussing.
    Ahhhh now we're getting somewhere - the third type of scenario I've described, where the input has a higher frequency than the natural damped frequency of the system.

    First of all, we're not discussing "harmonic resonance." That occurs when the forcing function is at the natural damped frequency of the system. What we're actually looking at is the response of the system to a single ramp type function perturbation.

    In this case, the system responds at its natural frequency. That's why when you go over the bump very slowly, your fork compresses very little, right? You simply move up with the wheel. Its acting nearly statically. At higher speeds beyond the natural frequency, you're bumped up off the ground - because the fork can't respond as quickly.

    In engineering terms, the rise rate of the system is too slow to accomodate the input so it lags. This is because the frequency response is too slow. Thus, you want less damping to raise the natural frequency.

    Going to the link you gave me makes me realize that you are looking at these bumps as a steady, consistent, repeating motion.
    No, I'm not, and if you look below where I gave you the link, I pointed out to you that that illustration shows frequency response due to a sinusoidal input, and that the actual system we're describing is under a single forced impulse, remember? The point of that image was to show you that the system is the same as if the ground weren't moving - the same equation is used. I also used it to illustrate what the term "base excitation" means, and why it doesn't matter in analysis.

    If that were the case then these concepts (Harmonic resonance, frequency response, out of phase) would be pretty much all we need.
    No. Go to any textbook, and answer the question I've repeatedly asked of you. What is the response of a spring, mass and damper system to an impulse input?

    I believe you'll find that it oscillates at its own natural damped frequency. In the case of a critically or overdamped suspension, it will oscillate "once," but it will oscillate.

    The image shows a system perturbed by a sinusoidal input. The difference is that any linear system driven by a harmonic input will oscillate at the frequency of the input.

    Its germane to this discussion, but I have pointed this difference out to you several times.

    But even with street cars and motorcycles there are other factors to be dealt with. Forces where it is the amplitude, not the frequecy that is the issue (a 6" deep pothole) This is especially true of mountain bikes. You are going to need something besides these few formulas to describe what happens as you plow over randomly distributed roots. Or a single root.
    So in other words, there's "new" forces at work? You're telling me that there's more than simply momentum, the perturbation force, damping, and spring at work?

    Here's the equation again. "F" is the forcing function from the ground. The other forces at work are as follows:

    mx'' = the change in momentum of the mass (rider and bike)
    -cx' = the damping force, proportional to velocity
    kx = the spring force

    If there's another solution to this problem other than the ones in, well, every textbook on the subject on my shelf, let me know and we'll get a paper peer reviewed immediately

    Or, how about this. We just accept that the difference between a motocross bike and a MotoGP suspension is really that the spring and damper rates are tuned for different types of frequency response across a certain bandwidth.

    Now, there's dynamic differences in things like suspension set up, linkages, etc. But the underlying math and physics are the same. Or, well, we wouldn't send people to school to study them.

    Of course the response frequency has SOMETHING to do with the behavior of the fork. I think your example of hitting a root at different speeds was acurate to a certain extent.
    I assure you it is. Its a textbook example.

    There are certain speeds at which an improperly damped fork will actually magnify the effects of the root. I think many of us have experienced this. However, in the example of hitting a root at high speed, we are talking about a properly damped fork at a speed far beyond the resonant frequency.
    Here, you're close, but missing the point again. If you hit a root above the natural damped frequency of your fork, no matter how "properly" damped it is, then its going to propel you into the air because the system can't accomodate it quickly enough.

    This is your suspension "sacking out," or not being able to rebound quickly enough. The frequency response is too low.

    "Properly" damped is a misleading concept. The inputs you get from the ground cover a wide spectrum of frequencies. There will always be inputs above or below the frequency of your fork and you tune as best you can.

    The second order model does fit into this as well, and you are correct that you cannot escape it.
    No more than you can gravity

    However, I do not think you are applying it properly. I am speaking of your assertion that initial velocity is the sole determination of how far the shock compresses.
    I don't see why - its an academic problem. Put two spring-mass systems of identical k and m next to each other. Push one down half as far as the other and let them go.

    They oscillate at the same frequency, right? Which one is traveling faster as it passes the equilibrium point?

    If you don't believe me, what's the derivative of the solution of the equation of motion? When is its value greatest? Hint: solve for x=0.

    I don't think you followed my example. Your model of a mass dropping on a damped spring DOES model a drop fairly well. It does NOT model hitting a root at speed very well. I don't see how you can get around the initial shaft velocity being very high when you hit a 2" root at 15 mph. Show me where my math was significantly off.
    Show me how your math takes into account your motion upwards, as the bike and the rider. It does not.

    Let's increase the damping sooo much that you have a notionally rigid fork. Are you accelerated upwards as the wheel goes over the root or not?

    Let's let it compress a little. You're still accelerated upwards, aren't you?

    Let's let it compress a lot. You don't disappear. You're still accelerated upwards, aren't you?

    F=mx"-cx'+kx. That's all you need to know.

    You seem to think that the bike accelerating upwards changes this. Fine, it does accelerate, but it accelerates from REST.
    That makes absolutely no difference. You're now grasping at straws here Come on, you measured the rise of the wheel hub over a distance and assumed the fork would be compressed that much. That's not even nearly realistic.

    If you put a mass on a spring and place it in the palm of your hand, then push up on it, what happens to the spring? Wait, we've been through this several times. Let's look at it mathematically again, in simple terms.

    F = the force of the ground.
    mx" = the momentum of the mass
    -cx' = the damping force, proportional to velocity, but opposing it in direction.
    kx = the spring force.

    The force of the root pushing up on the wheel and fork lower is balanced by al of these things, right?

    Just as an academic exercise, think about pushing up on the spring, forcing x to increase. What happens to the rest of those terms? What difference does it make if k is really low as a soft spring, or high as a stiff spring? What about c, the damping ratio?

    At the first small moment after the impact, the wheel is travelling very fast and the bike is just beginning to accelerate and is going very slow. The difference in these speeds is the shaft velocity and it is higher that that seen in a drop.
    No, its not higher. It only appears to be higher to you because it has a much quicker frequency. You're comparing apples and oranges by coming up with meaningless comparisons between this distance and that distance, and fork compression.

    The only variables that matter are time and fork compression.

    Now I want you to think about this statement very carefully. You'll never get your fork to compress faster than its natural frequency response. You will always be propelled upwards to make up the difference. Always. This is why the faster you go, the more and more you're popped up rather than the fork just compressing more and more.

    Acceleration is not an instantanious incease in velocity, is a gradual one. This is especially true if it is due to being pushed by a spring. The front wheel accelerates upwards at a FAR greater rate than the bike does (the tire is a MUCH stiffer spring that the shock), and the higher the tire pressure the faster the acceleration.
    That's entirely dependent on the natural frequency response characteristics of the spring. If its a very low frequency input compared to the bike's natural frequency, then the bike will go up almost exactly as quickly as the wheel hub.

    Think about it. Stiffen the spring - this raises the natural frequency. If its so high of a spring constant that we now have a rigid fork - your bike will accelerate at a rate arbitrarily close to that of the wheel hub!

    As a matter of fact, this absolutely holds true for rigid forks as well! If we take an average cross sectional area of the fork and multiply it by the elastic modulus of the material, then divide by the length, we have the spring constant of your rigid fork as a beam in longitudinal compression. This gives you a very high natural frequency, since its proportional to the square root of k.

    Now, nearly all inputs are "low frequency," so the bike will respond statically to being pushed up. The bike is always in phase with its inputs!

    Seems to me like the equation may be universally applicable after all

    OK, so if this is the case (the shaft velocity is greater than in a drop), why doesn't the shock compress more from this high initial velocity than the lower velocity seen in the drop?
    Because the velocity isn't higher, you've just convinced yourself it is.

    At first glance the second order formula seems to say otherwise, and I think this is what you are stuck on.
    Well, there's a reason I'm stuck on Newtonian physics - they describe all motion. So are all other engineers.

    What I think you are missing is that once the root is cleared the variable for mass is greatly reduced, and you need to re-work the formula using this new mass.
    Ahhhh...no. Nice try, but it doesn't work that way.

    What I believe you will get is a motion that is slowed down much more quickly and does not reach the same amplitude.
    Well, no. Once you're off the ground you get parabolic motion centered about the bike's center of gravity. But the movement of the bike prior to that is absolutely described by the equation of motion.

    That's neither here nor there. What we're looking at is the compression of your fork - which is different.

    Clearly the forces present as the wheel was being pushed upwards for the first two inches are very different now. Now all you have is a 5 or 6 pound mass traveling upwards to slow down. (iI'll get to your spring in hand example below which is, I believe, completely consistent with what I am saying here)
    You miss the point. If the frequency response of your system was fast enough, then you wouldn't be propelled upwards off the ground at all. Is your fork going to compress more and more as you take that bump faster and faster? Or are you going to get propelled more and more up into the air?

    I think its the latter. As a matter of fact, physics agrees with me, as we'll see in my rigid fork example below.

    THINK you may be working backwards on this. I THINK what you are doing is looking at that fact that a shock does not compress as far on a high speed hit on a root as for a drop, and determining that the initial velocity MUST therefore be less.
    *sigh* No, not at all. Look, go back and think about this again. What's the difference between hitting the root at low speed versus high speed? How does your fork's response change as you increase speed?

    And, importantly, at what point will your wheel begin to leave the ground as you hit it?

    Hint: at the natural damped (resonance) frequency of your suspension system.

    Now, think about it. As you go faster and faster over the bump, you're pushed upwards at a rate that approaches the same rate as the wheel more and more. Your suspension compresses won't compress any more no matter how much faster you hit it, you'll just be pushed up more.

    In engineering terms, at this point the momentum force is overwhelming the spring force, and the spring can't "push" the mass as fast as the driving input - hence its 180 degrees out of phase. Prior to this, the spring force is overwhelming the momentum force. Remember the rigid fork example? (At resonance, the two are equal, and the real part of the frequency response goes to zero as the imaginary part takes over the plot.)

    You use the second order formula to back this up, but you are not taking into account that a key variable changes part way through the scenario: The mass that the spring is dealing with. I think that if you re-worked the equation with this, you would find that you CAN in fact have a higher initial velocity and yet have a shorter total compression.
    No. You can't. Sorry, its physics, not me

    I am saying that a root hit at high speed causes a very high initial shaft velocity, and yet it does not cause the shock to compress as much as the lower speed drop.
    Well, I don't know what to tell you other than you're wrong. Not only that, but I would submit to you that based on the boundary conditions of the problem you cannot compress your fork by any hit faster than its natural frequency allows. This is also based on simple physics and balance of forces.

    This was the entire point of my last post. You just described WHY such a fast hit causes my bike to buck and the wheel to not return to the ground fast enough. Great, a clear and concise aplication of resonance theory, but what is your point? You just decribed what I am saying happens in great detail.
    I'm not describing resonance. I'm describing the frequency response of a linear system to a simple impulse input.

    As I've described above, not only does the standard equation of motion describe the movement of your suspension fork, it also describes the motion of your rigid fork as a very stiff spring.

    Dude, these are fundamental concepts behind most of the areas of mechanical engineering and design. What do you think finite element analysis is?

    Its analysis of a bunch of spring elements joined at nodes, right? Entire buildings are analyzed this way, kid, let alone suspensions.

    Notice that you needed a DIFFERENT example for hitting a root than for landing a drop?
    No, I didn't.

    Of course all the rules of resonance, second order equations, and frequency response apply to both, but the practical results are different. It's apples and oranges.
    No, it really isn't Otherwise, I'd be pretty bad at my job.

    Let's look at the spring-in-hand example. Had you lifted your hand and kept lifting it at a steady rate, then motion of the spring with the mass on top would very much resemble the motion caused by a drop, and would be neatly explained as a second order motion. But that is not what you are doing. You are quickly lifting it AND THEN PULLING YOUR HAND BACK DOWN.
    *sigh* You're now confusing transient response with steady state response.

    But if you want to play that way, fine.

    Take a spring and a mass, again.

    Put one on the ground. Drop the other from as high as you'd like, and push up, pull up, or otherwise perturb the other however you feel like.

    Tell me how their transient and steady state responses are different.

    Here is another problem the second order equation runs into in the real world when you use it to model motion. The damping on forks is nothing close to constant. Rebound and compression are often set at vastly different levels. Comression damping may vary with position (position sensitive damping) or shaft speed (speed sensitive damping), Well, OK the shaft speed is still being debated here.
    Now you're just flat out guessing. The only difference having different compression and rebound damping would make is that the sine wave would have slightly different "halves." The only difference variable damping makes is that at different times, you have different frequency responses.

    And if you noted, I pointed this out to you repeatedly. All of these things are done to tune frequency response for a desired effect.

    We do this in mountain bike suspensions, motorcycle suspensions, building elements, structural applications, you name it. Seriously. This is what I do.

    As I said, I agree that the second order formula will always work, but it is far more complicated than plugging in one set of numbers and leaving it at that. Real world factors mean that these variables (mass and damping) are constanly changing, and in this case comparing a drop to a root is apples and oranges.
    No. The difference is only in the details - I mentioned repeatedly that these schemes change damping for desired affects.

    As to the question of high speed dampers responding to frequency: There seems to be another debate going as to on whether they respond to pressure or velocity. My veiw is that the two are linked, and one is the function of the other.
    Of course they are. But viscous damping is proportional to velocity - this is the -cx' term.

    Its better to think of it that way.

    I am still scratching my head as to which is a function of which, but they do vary together, though not proportionally.
    They are proportional. Seriously.

    Let's leave out a large discussion on momentum transfer, viscocity, and how orifices work and settle for the obvious.

    If your spring has no air in it, its easy to push your fork slowly, right? Its hard to push it fast.

    As a matter of fact, the force with which your fork pushes back at you is linearly related to the velocity with which you push it. This is why my Epic will sag over 30 seconds. If you try to force it down, it ain't moving. But it'll let a force push it down very slowly.

    Its all about balancing the forces - or, F=mx"-cx+kx

    Whichever one the high speed valve responds to, both can vary independent of frequency.
    It varies - but the natural damped frequency remains the same regardless of velocity or amplitude. Remember the damped natural frequency is simply related to the natural frequency as follows: (Natural Frequency)*sqrt(1-(Damping ratio)^2).

    Think of a fork moving up and down 1 inch 5 times per second. The frequency is 5Hz. Now, move fork up and down 5 inch 5 times per second. Same frequency, 5Hz, but the oil pressure, or velocity, (whichever you claim opens the valve) is WAY higher.
    Yes, the linear displacement x is higher. And the frequency stays the same so long as damping stays the same.

    As a matter of fact, in the example you just made, the velocity out of equilibrium is a whole lot faster in the example than where its compressing much further, isn't it?

    But seriously, think about it, it makes sense. Go back to the equation of motion and its solution.

    In the middle of the sine wave, velocity is at its max. But so is the damping force, because its proportional to velocity and opposite in direction. This means that if you have a big sine wave or little sine wave, the damping force is always proportional to the rate of displacement, so the amount of displacement can never change the frequency of a viscously damped system.

    Now, the corrolary to this is that you tune your frequency response via damping. If you increase your damping ratio, you will lower the natural frequency of your fork to something less than 5Hz.
    Last edited by TXNavy; 02-16-2005 at 04:30 AM.

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    wow

    You have got beyond my high school physics. Even Dougal has stayed out of this one, and he usually eats this for breakfast. lol Jim

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    Quote Originally Posted by kapusta
    (D8 mentioned something about direction of force, but the shock is going to respond to the force along IT'S line of shaft movement. As I said, I did assume the shaft to be straight up and down, but I think my number are at least in the ball park. D8, If you have significantly different numbers, show how you get them)
    I'm too lazy and disinterested in correcting everyone on the math when there's a MechE major doing it already, but you can see the difference in shaft movement vs bump size on bikes with adjustable geometry (or forks with adjustable travel which doesn't alter the fork rate or damping setup). Changing the head angle of the bike also alters the angle at which the fork encounters a bump. So ride over the same bump with the head angle set different and you can see the change in fork compression. For that matter, this is why LINKAGE forks like Amp forks and Girvin/Noleen forks respond better to head on impacts like rocks and roots, than drops. The axle path moves backwards and upwards in an arc, not simply diagonally like on a telescopic fork.
    I don't post to generate business for myself or make like I'm better than sliced bread

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    you guys are getting sidetracked debating the spring model

    What we are concerned about is the damping system - hi-speed low-speed, threshold whatever
    Picture an oil filled cylinder lying on it side, a piston inserted in one side, and a small hole or orifice damping mechanism at the other end of the cylinder .
    Hit or push the piston, and what happens at the opposite end of the cylinder? No spring is required for this model.
    Your spring and dropping weight model may simulate a drop, but for the 2" root you would have to put your spring in a cylinder so that only the top 2" protrudes from the cylinder, now drop a block of ice - the ice will compress the spring 2" then shatter when it hits the outside edge of the cylinder. Even if the ice block hits the spring in the cylinder at a much higher velocity (such as for a root) than a slower hit for an unsheathed spring (such as a drop) the spring in the cylinder can only compress 2" whereas the unsheathed spring can compress fully.
    Large motor vehicles can wallow or bounce up and down for a while after hitting a bump (until the minimal damping stops the bounce). But bikes and riders are a smaller mass, and use relatively highly damped shocks, so for the same bump the motor vehicle hit you will experience negligible wallow (and probably an upwared spike to your body because the bikes damping did not allow the spring to compress fast enough). Which supports my idea that its the damping and not the spring thats important for us.

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    Uhhh. No.

    It *always* works the same. Viscous damping does two things. It reduces the natural frequency to the natural damped frequency, by a factor of sqrt(1-(Damping Ratio)^2). It also adds an exponential decay to the oscillation. In a critically or overdamped application, the system returns to equilibrium without oscillating past the equilibrium point.

    Cars are not intended to "wallow," nor are bikes "more damped." Well, unless perhaps your car has a broken damper They have damping proportional to their spring rate and mass, which makes sense. Moreover, mountain bike spring rates are proportionally set the exact same way car or motorcycle spring rates are. If bikes had way more damping than they did spring, they would always be overdamped. They would always have a very low frequency resposne to input, and be unable to deal with lots of small bumps. This leads to "sacking out." In point of fact, off road applications typically have less damping in proportion to automobiles and other on road applications, for just this reason. What's "bouncier," a Jeep or a BMW?

    In actuality, off road applications including mountain bikes have both softer (lower) spring rates and lower damping ratios - not higher.

    Remember the linear system model, and do the balance of forces on the bike. You're balancing the input force with three other forces: momentum, damping force, and spring force. This is why suspensions are typically used as textbook examples in physics and vibrations courses. They're easy to understand and apply basic concepts such as frequency response, rise time, settling time, etc.
    Last edited by TXNavy; 02-16-2005 at 01:42 PM.

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    ...and just to point out further how "real world" accurate this is, let's expand the model. So far we've restricted the discussion to a single degree of freedom (1-DOF) model. We can easily expand to include both ends of the bike AND the tires!

    Consider a 2-DOF model, with up and down motion like we've described but on two springs fore and aft. Up and down is "pure translation" motion. But obviously, the model can also rotate back and forth on the springs. This is "pure rotation." This system will have two natural frequencies, one for each mode of motion, and ALL possible motion by the system can be described by a linear combination of the two modes.

    We can even add another set of springs and dampers below the first springs - to simulate the tires. All this does is modify the frequency. If we wanted to make it 3-DOF for the angles of the suspension, we could do that. Or we could simply change the spring and damper rates according to the angle and leave them as straight vertical. Its pretty easy.

    This is, actually, a fairly typical homework problem for an undergraduate engineer. At any rate, we now have a pretty accurate finite element model of the bike suspension. It would be pretty easy at this point for me or another engineer to plug it into NASTRAN or other software to explore these properties we've discussed.
    Last edited by TXNavy; 02-16-2005 at 06:14 PM.

  90. #90
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    Quote Originally Posted by kapusta
    I would consider a drop pretty slow compression. I did some fiddling with the 9.8 m/sec2 formula and a 4' (1.33 meter) drop. If I did this right, your initial downward velocity when you hit the ground on a 4' drop to flat (which is a pretty hard hit) is ~.52 m/sec or 18.7 in/sec. Raise it to 6 feet (that is pretty big if you are dropping to a flat) and that speed is .64 m/sec or 23 in/sec. I don't think either of these speeds are very high. Another calculation I did was convert mph into in/sec and got 1mph = 17.6 in/sec, so if you are traveling at even 10 mph that is 176 in/sec.
    I think your figures are a little out.
    Falling velocity is = sqrt(2*g*h).
    A 1 metre drop equates to 4.4 m/s which is a pretty high speed impact.

    I can't be bothered reading the other posts, but I will throw in that the constant, linear damping used in the mathematical model is only an approximation. Real dampers with truely linear damping are hard to find.
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
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    Oops!

    Quote Originally Posted by Dougal
    I think your figures are a little out.
    Falling velocity is = sqrt(2*g*h).
    A 1 metre drop equates to 4.4 m/s which is a pretty high speed impact.
    \
    Oops! I divided by 2 instead of multiplying. Dooohhhh!

    So uhhhhh...mmmmm...NEVERMIND!

    Thanks, but dude, where were you three days ago? ;^>

    And why the #@$%#$ did 3rd-year-engineering-school-man never mention this in our last 40,000 lines of debate?

    Yeah, so, I guess I will change my mind on the drops-being-low-speed-hits-thing.

    Thanks
    Kapusta

    P.S. TXNavy, I still think you are wrong ;^> But seriously, our whole debate has just become a rather moot point to me. It was fun, though. Let's do it again.

  92. #92
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    Quote Originally Posted by kapusta
    P.S. TXNavy, I still think you are wrong ;^> But seriously, our whole debate has just become a rather moot point to me. It was fun, though. Let's do it again.
    Well, its a free country So long as your suspension works as you expect it to you'll be happy...

    Regards,
    Patrick

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    hmmmm, my bad for confirming the drop hit speed calculation. I guess that clears some things up, even if they are highly idealized calculations in the first place: i.e. 90 degree head angle....

    Also, don't mistake TXNavy for a 3rd year major, he stated he's a MASTER'S student, definitely beyond undergrad shenanigans.

    TXNavy, are you sure you can't borrow those accelerometers? I'd really like to see results of riding forks of varying quality over a given terrain, plus it would be very nice to see exactly what the real frequencies of drops, roots, and rock gardens all look like on a given fork.

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    OK, That's IT!!!!

    I just ordered a Pike Team. I got it with the Poplock for $435. Not sure how I feel obout another thing on my bars, or the blue color, but it was such a good deal I figured what the heck. Gonna build my new wheel on a 20mm Marzocchi Hub. Can't wait to do all those HIGH speed drops. Great thread Microhuck!

    Multiply by 2: Good!...Divide by two :Bad...
    Multiply by 2: Good!...Divide by two :Bad...
    Multiply by 2: Good!...Divide by two :Bad...
    Multiply by 2: Good!...Divide by two :Bad...
    Multiply by 2: Good!...Divide by two :Bad...
    Multiply by 2: Good!...Divide by two :Bad...
    Multiply by 2: Good!...Divide by two :Bad...

    Kapusta

  95. #95
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    Quote Originally Posted by carlo
    hmmmm, my bad for confirming the drop hit speed calculation. I guess that clears some things up, even if they are highly idealized calculations in the first place: i.e. 90 degree head angle....

    Also, don't mistake TXNavy for a 3rd year major, he stated he's a MASTER'S student, definitely beyond undergrad shenanigans.

    TXNavy, are you sure you can't borrow those accelerometers? I'd really like to see results of riding forks of varying quality over a given terrain, plus it would be very nice to see exactly what the real frequencies of drops, roots, and rock gardens all look like on a given fork.
    Which reminds me. I must chase up the geek (electrical eng student) who's building my data logger. My serial fed laptop one is only good for 3 second bursts and is too sensitive to vibration.
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
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    Could be worse. It could be from the eighties and sensitive to UV light flicker like our equipment

    (Almost all of our serious work by the vibration guys is simulated on the total ship level, so lab work is kind of lacking for thesis money around here...)

  97. #97
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    Quote Originally Posted by MicroHuck
    Here's a Motion Control explanation guide. Even the rockshox representatives don't know this stuff. I think RS should be giving people more info about it, then they might be more inclined to consider it when they realize how great it really is...

    I rode the stock spring for a week and was able to get it to not use full travel on jumps by adjusting the floodgate, it makes a huge difference. I weigh 180.

    BTW, anyone who buys the PIKE should break it in good before switching to a harder spring.

    Here's why the fork goes through it travel so easy even with the right spring:

    The floodgate control is exactly like Marzocchi's HSCV (high speed compression valve). It remains closed until there's enough pressure to make it flip open and allow more fluid to flow. The floodgate adjuster on the PIKE allows you to change how much pressure is required to move the valve open. When you have the floodgate totally loose it requires ZERO effort to open it up so adjusting the compression knob to full closed still doesn't do anything to slow down the fork because the floodgate is overiding it and letting too much fluid through, thus no compression damping.

    The floodgate valve is always working whether you have the compresion knob open or closed or anywhere in between. This is why it is considered a high speed comression valve. When you put the fork in lockout mode the compression damper is completely closed, so you are pushing entirely on the floodgate spring valve. This is why the fork maintains the ability to adjust it's SPV type lockout and the pressure reuired to move on bumpb but stay locked for no bobing. YOu have to adjust the floodgate in order to get the desired amount of lockout when the compression knob is closed.

    If you are dirt jumping I would put the floodgate valve completely closed tight, that way the compression damping does it's job in slowing down the fork on hits. You then want to put the compression knob wherever you want, usually halfway.

    When you hit the trails, you want to put the floodgate knob full open and the compression full open if you're not doing any drops. This will make the fork respond incredibly fast no matter what high speed you're riding at.

    Pretty cool huh? The PIKE's motion control is pretty much like a fully adjustable HSCV cartrdige AND a SPV chamber in one unit, but is still more adjustable than both! I also think Motion Control feels and works better than SPV, plus it requires no air.

    The idea behind that red swiss cheese thing in the PIKE's damper is this:

    The compression unit and the floodgate sit at the bottom of that red thingy. The red swisscheese thing is actually a rubber spring that allows for 20mm of plush movement. This make it so that when you lock out the compression attached to the bottom of it, it still is allowed to move 20mm by compressing the rubber piece. This helps give the lockout a better transition from locked to the floodgate valve being forced open on a hit and allowing for fork movement. Very cool idea! Very simple too and light weight!

    The rubber tube does a second task even when the fork isn't locked out. It allows for the compression unit to react quicker to super fast and square edged hits by allowing 20mm of movement without oil being forced through the compression/floodgate unit. This allows for the compression/floodgate enough time to open without any delay in fork compliance. It takes a micro second for the floodgate to open, but the rubber piece reacts instantly thus making it smother on REALLY fast hard square edged hits. This is similar to having a shimmed damping system like TPC. It is also why most people say it feels just as smooth or smoother at high speeds than TPC, HSCV, AND FOX's damping system.

    IMO, the MOTION CONTROL SYSTEM is a very revolutionary concept to biking. You can really tell they thought outside of the box on this one. Not only did they create the most versatile damping system, it;s also lighter, more simple, and cheaper to build than any other comperable system.

    VERY COOL!
    Hey MicroHuck,

    Thanks for your detailed analysis and input on the motion control system. I am currently in the market to buy a Pike fork for my Azonic Saber. I am about 195lb. ride weight and primarily ride aggressive trail/all-mt. stuff with no drops greater than a couple of feet. I am unsure as to whether get the Team model with the external floodgate or the SL with an internal floodgate control. I am leaning towards the SL, to save a few bucks so I can buy a new hub and wheel build, but wouldn't mind saving a little weight since my trail bike comes in at 32.8lbs. with a light air fork on it right now. What model would you recommend for my bike and riding needs?
    Thanks again for taking the time to break things down, a fellow NW rider, jon.

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    Quote Originally Posted by jgusta
    Hey MicroHuck,

    Thanks for your detailed analysis and input on the motion control system. I am currently in the market to buy a Pike fork for my Azonic Saber. I am about 195lb. ride weight and primarily ride aggressive trail/all-mt. stuff with no drops greater than a couple of feet. I am unsure as to whether get the Team model with the external floodgate or the SL with an internal floodgate control. I am leaning towards the SL, to save a few bucks so I can buy a new hub and wheel build, but wouldn't mind saving a little weight since my trail bike comes in at 32.8lbs. with a light air fork on it right now. What model would you recommend for my bike and riding needs?
    Thanks again for taking the time to break things down, a fellow NW rider, jon.
    Get the SL and make your own knob for it. It's also very easy just to have a 2.5 hex wrench taped to your handle bar. Since you won't be adjusting the floodgate very often you can just use a hex wrench. The rebound knob comes out and is a hex wrench too. I would only use that when nothing else is around, it doesn't like being taken on and off constantly. If you don't care about the extra $30 just get the RACE and no worries, all set to go. The RACE is still a dirt cheap fork!

    -----------------------------------------------------------------

    I seemed to have forgoten about the rebound control in MC damping. Nothing complex. It's just that the thing has the most range of adjustability I've ever seen on a rebound unit. You can get that rebound SUPER slow (2 seconds to rebound, that's slow!) for big hits. You can also set it to have NO rebound control.

    The pike doesn't have a shimmed rebound damper though. IMO, that's actually a good thing to not have in such a versatile fork. Shimmed rebounds like my TPC sherman flick are too damn bouncy for drops and hard hits, I can't get the rebound slow enough. TPC rebound is only good for rockgardens, otherwise I think it sucks for freeriding where you need uber slow rebound for drops. This also goes for Dirt Jumping. The great thing about Motion Control is that you can also set the rebound fast for trail riding.

    -----------------------------------------------------------------

    Funny how all the guys who kept insisting I was wrong about a 4 ft drop being a high force event, have shut up! You guys can talk speeds all you want, but in the end all that counts is that HSCV opens up the high speed valve on even small drops. Just yesterday I saw TWO Super T's bottom out on a 4.5 ft drop. A 170mm fork doesn't bottom out that easily unless it has lost significant amounts of compression resistance. My buddy's Drop off 2 SSV 130mm fork still has an inch left of travel on the same drop.



    SO FOR THE LAST TIME!:

    You NEED to close the floodgate significantly on the PIKE/REBA forks in order to prevent excessive travel use on hard hits. Other wise the floodgate will open up at low pressures and flow too much oil, thus a loss of compression damping. I just close it all the way for jumps/drops, then move the compression knob 1/4 to 1/2 of the way up. I guarantee you won't bottom out the fork in those settings.

    If you want your fork to be IDENTICAL to an HSCV fork do this:

    Turn compression knob to full closed. Then adjust the floodgate so that you can feel it resisting, but opens up when you push down on the fork. Now open the compression knob to halfway or 2/3 of the way. You now have good low speed control AND the floodgate will flip open on faster/harder hits to give you high speed ability too. This is a good setting for XC use and all around use.

    If you want your fork to just eat through everything in front of you do this:

    Open floodgate and compression to full open/loose. There's nothing better at super fast speeds and nearly no compression damping.

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    HERE'S A LINK ON HOW TO MAKE YOUR OWN SL EXTERNAL FLOODGATE KNOB FOR LESS THAN $2.00!

    KNOB INSTRUCTIONS

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    TXNavy-

    Thanks for spending the time to give us some info on the dynamics of forks. I thought I was the only one who spent good time writing posts.

    Just one question though, are we talking about a chunk of metal that moves up and down OR are we talking about a system for sending bikers to the moon? Your info has my head spinning. Better get NASA to crunch those numbers for us!

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    Here's some footage of the PIKE in action. This is how it does freeriding! This is me riding in my freeride stunt course. No one else was around so I had to click the camera timer and jump dozens of times, then I compiled the images for a sequence.

    BTW, I ride a Hardtail with the PIKE. The PIKE is excellent on hardtails due to the range in travel. My bike can go from DH hucker to XC ripper just by lowering the fork and rasing the seat. Lowering the fork is also good for Dirtjumps, it also helps put more stanchion into the lowers for more durability and stiffness.

    Last edited by MicroHuck; 02-20-2005 at 10:26 PM.

  102. #102
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    Quote Originally Posted by MicroHuck
    Get the SL and make your own knob for it. It's also very easy just to have a 2.5 hex wrench taped to your handle bar. Since you won't be adjusting the floodgate very often you can just use a hex wrench. The rebound knob comes out and is a hex wrench too. I would only use that when nothing else is around, it doesn't like being taken on and off constantly. If you don't care about the extra $30 just get the RACE and no worries, all set to go. The RACE is still a dirt cheap fork!

    -----------------------------------------------------------------

    I seemed to have forgoten about the rebound control in MC damping. Nothing complex. It's just that the thing has the most range of adjustability I've ever seen on a rebound unit. You can get that rebound SUPER slow (2 seconds to rebound, that's slow!) for big hits. You can also set it to have NO rebound control.

    The pike doesn't have a shimmed rebound damper though. IMO, that's actually a good thing to not have in such a versatile fork. Shimmed rebounds like my TPC sherman flick are too damn bouncy for drops and hard hits, I can't get the rebound slow enough. TPC rebound is only good for rockgardens, otherwise I think it sucks for freeriding where you need uber slow rebound for drops. This also goes for Dirt Jumping. The great thing about Motion Control is that you can also set the rebound fast for trail riding.

    -----------------------------------------------------------------

    Funny how all the guys who kept insisting I was wrong about a 4 ft drop being a high force event, have shut up! You guys can talk speeds all you want, but in the end all that counts is that HSCV opens up the high speed valve on even small drops. Just yesterday I saw TWO Super T's bottom out on a 4.5 ft drop. A 170mm fork doesn't bottom out that easily unless it has lost significant amounts of compression resistance. My buddy's Drop off 2 SSV 130mm fork still has an inch left of travel on the same drop.



    SO FOR THE LAST TIME!:

    You NEED to close the floodgate significantly on the PIKE/REBA forks in order to prevent excessive travel use on hard hits. Other wise the floodgate will open up at low pressures and flow too much oil, thus a loss of compression damping. I just close it all the way for jumps/drops, then move the compression knob 1/4 to 1/2 of the way up. I guarantee you won't bottom out the fork in those settings.

    If you want your fork to be IDENTICAL to an HSCV fork do this:

    Turn compression knob to full closed. Then adjust the floodgate so that you can feel it resisting, but opens up when you push down on the fork. Now open the compression knob to halfway or 2/3 of the way. You now have good low speed control AND the floodgate will flip open on faster/harder hits to give you high speed ability too. This is a good setting for XC use and all around use.

    If you want your fork to just eat through everything in front of you do this:

    Open floodgate and compression to full open/loose. There's nothing better at super fast speeds and nearly no compression damping.
    Micro, I don't think anyone was arguing that drops were low FORCE. The debate was over SPEED not force. And of course we all shut up when my glorious speed calculations for a drop were shown to be out the window. The debate would have been over much sooner if someone besides me had done the math ;-> So far as the valve reacting to speed or force or pressure or whatever....I think we all got just tired of talking about it.

    BTW, if someone bottomed out a super T on a 4-1/2' drop, they did not have it set up right, or they landed terribly.

    Kapusta

  103. #103
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    Quote Originally Posted by kapusta
    Micro, I don't think anyone was arguing that drops were low FORCE. The debate was over SPEED not force. And of course we all shut up when my glorious speed calculations for a drop were shown to be out the window. The debate would have been over much sooner if someone besides me had done the math ;-> So far as the valve reacting to speed or force or pressure or whatever....I think we all got just tired of talking about it.

    BTW, if someone bottomed out a super T on a 4-1/2' drop, they did not have it set up right, or they landed terribly.

    Kapusta
    both were 2003 Super T and were going through all of travel. I suggested to them that they should switch to heavier oil and raise the level a bit. They were not clunking hard on the 4.5ft drop, but were going through most of the travel. People have complained about this on the FR Series the most. I think the two SupT's I saw were setup wrong which compounded the effect of the damping change. As I understand, the SUpT has compression adjust, where as the Freeride (non ssv ssvf) series and Marathon Series have no compression adjust, correct? This would explain the many complaints of people who own the HSCV FR 130 and 150 forks, that claim it blows through its travel so easily.

  104. #104
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    Quote Originally Posted by MicroHuck
    both were 2003 Super T and were going through all of travel. I suggested to them that they should switch to heavier oil and raise the level a bit. They were not clunking hard on the 4.5ft drop, but were going through most of the travel. People have complained about this on the FR Series the most. I think the two SupT's I saw were setup wrong which compounded the effect of the damping change. As I understand, the SUpT has compression adjust, where as the Freeride (non ssv ssvf) series and Marathon Series have no compression adjust, correct? This would explain the many complaints of people who own the HSCV FR 130 and 150 forks, that claim it blows through its travel so easily.
    Well where to start.
    The behaviour you observed (using all the travel without loud clunking) is <b>EXACTLY</b> what you want off a 4.5ft drop. Increasing the oil level and viscosity would make your 170mm travel fork feel like a 140mm travel fork (or less).

    There's no point in having travel you can't use. I can almost imagine the thoughts running through their heads and none of them would be favourable to you.
    If you can't use all your travel on a 4.5ft drop then when the hell can you?

    You also seem to miss the whole point of speed sensitive damping. The damping is more linear with speed and doesn't spike. The only dampers which behave like your truncated hyperbola are the cheapest and crappiest imitation of a true speed sensitive damper. Search the net for a few shock curves off a dyno and you'll eventually work it out.
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
    www.dougal.co.nz

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    so Dougal you are basically saying that the high speed valving opens proportionally to speed/pressure (which makes sense and is what i thought) so that hopefully you will use as much ravel as you can on anything between a 2ft and a 10ft drop?!?

    what stops the fork bottoming harshly in these cases?? (this is a genuine question as i dont know) Is it because as the oil flows, the pressure decreases until the high speed valve effectively closes and this ramps up the compression meaning the fork doesn't bottom?

    i know this is off topic but i may aswell ask it here

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    amusing thread

    Well I've just skimmed through this thread and enjoyed a few good laughs along the way. The highlight for me was Dougal pointing out the error in the use of Newton's equation of motion for calculating impact speeds from a drop. Highly amusing!

    Large drops and square edged hits will both create large damper velocities at differing amplitudes. On a drop the damper is controlling movement of the sprung mass (bike + rider), while on a square edged hit over a rock or root the damper is controlling movement of the unsprung mass (wheel + lower half of the fork). These masses are obviously very different magnitudes and have a very big effect on the system respone in each case. I don't know if this was mentioned at some point in the thread. I didn't notice if it was.

    Anyway, I'm looking forward to someone gathering some decent displacement/velocity traces from an actual bike in action. I know Dougal is quite close to achieving this with his homemade data logger. It's not exactly rocket science to attach a linear pot or LVDT to the fork and shock and record some data. It's just time and money like everything else.

    By the way I started reading this thread because I have a Pike fork. I have the floodgate set fairly tight with the compression about halfway and it works just fine. I find it too harsh over smaller hits with the lockout fully engaged, although it does blow open fine over bigger stuff. I might play around with the floodgate setting more now I've read all this.

  107. #107
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    Quote Originally Posted by uktrailmonster
    The highlight for me was Dougal pointing out the error in the use of Newton's equation of motion for calculating impact speeds from a drop. Highly amusing!
    Yeah, I wish he had done so 30 posts earlier ;->

    Quote Originally Posted by uktrailmonster
    Large drops and square edged hits will both create large damper velocities at differing amplitudes. On a drop the damper is controlling movement of the sprung mass (bike + rider), while on a square edged hit over a rock or root the damper is controlling movement of the unsprung mass (wheel + lower half of the fork). These masses are obviously very different magnitudes and have a very big effect on the system respone in each case. I don't know if this was mentioned at some point in the thread. I didn't notice if it was.
    Oh, yes, it was mentioned. You have to be willing to go into those REALLY long posts to find it, but it was my central point in the debate between myself and TXNavey. Actually, I was saying that it was the "unsprung" mass after the root was cleared. Dig in there and you will find this discussed on all sides at length. It's good stuff (if you are a total geek like me)

    Kapusta

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    Quote Originally Posted by kapusta
    Yeah, I wish he had done so 30 posts earlier ;->



    Oh, yes, it was mentioned. You have to be willing to go into those REALLY long posts to find it, but it was my central point in the debate between myself and TXNavey. Actually, I was saying that it was the "unsprung" mass after the root was cleared. Dig in there and you will find this discussed on all sides at length. It's good stuff (if you are a total geek like me)

    Kapusta
    LOL thanks. When I get more time (like a few spare hours!) I'll re-read this thread in more depth. It does seem an interesting read.

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