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  1. #1
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    Can somebody explain high speed damping? (on forks)

    I sort of understand low speed compression damping. It is to help prevent brake dive and bobbing, as it gives a little bit of a platform feel. But I don't understand high speed compression damping. I know that it mainly occurs if you hit a big bump at high bike speeds, but I don't know whether you want a lot of it (perhaps to prevent bottoming) or a little of it to get more bump absorption and less shock transmitted to the hands. Should the (dyno) curve be steep or shallow, and what is the preload or y axis intercept? The only careful tuning I have done is on vehicle suspensions, and I know that in that case, I like a relatively linear curve (medium slope, low preload). If the curve is too digressive, the high initial slope makes small bump compliance feel bad. If there is too little high speed compression, the suspension also seems to get this rubbery feel.

    I sort of understand low speed rebound damping. It is to help prevent spring-back when you hit a big obstacle at slow bike speeds. But I don't understand high speed rebound damping. I know that it mainly occurs after you get launched off a rock or ride over a pothole, but again, I don't know what the ideal damping curve should be (for a given style of riding, ok?). The only careful tuning I have done is on vehicle suspension, and I know that in that case, if the curve is too digressive, you get this weird sensation where the car springs back quickly after a big dip, and then suddenly stops. It feels a little bit disconcerting, but maybe for bikes that is ok. It seems that digressive is the way to go to prevent "jacking down".

  2. #2
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    I only have a few minutes, so I can only post a few short things for now:

    High speed or low speed compression or rebound have nothing to do with bike speed, its about the speed at which the fork is compressing

    HSC is like a blow off of LSC. When oil cant flow through the LSC port fast enough, the HSC valve(usually shims) will open to allow more oil to flow. The more HSC you run, the less oil can flow during high shaft speed impacts.

    The more HSC you run, the more you will feel your fork(or shock) spike during high shaft speed impacts. This is caused by the oil not being able to flow past the compression piston fast enough and the fork/shock reaching the maximum shaft speed that the oil flow will allow.

    HSC can/is used to control bottom out. But can lead to the harsh spiking feel.

    There is no correct answer on how much to run, its all based on preferences. From my general experience, you want to run enough to keep high shaft speed impacts feeling under control, but without the spiking feeling you get from running to much.

    You mention preload. If you have a preloaded shim stack for a HSC circuit, its going to give a platform type feel when the LSC port is closed. Non preloaded shim stacks will always flow some oil, so no platform and a more linear damping curve would exist.


    For rebound, HSR is used to bypass LSR and help a fork/shock return to full travel fast enough to not pack up. Because the only force a rebound damper faces is the force of the spring pushing the fork/shock back to full travel, HSR generally happens deeper into the travel(higher spring pressure) while LSR happens at the beginning of the stroke(low spring pressure). This is not always the case, but its the general rule. Its also why LSR is often referred to as begging stroke rebound and HSR is referred to as ending stroke rebound.

  3. #3
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    Quote Originally Posted by mullen119 View Post
    High speed or low speed compression or rebound have nothing to do with bike speed, its about the speed at which the fork is compressing.
    Correct.

    Low speed shaft compression events:
    - Landing a jump
    - Braking
    - Big hits

    High speed shaft compression events:
    - Stutter bumps
    - Chipseal
    - Any small bump

    It's counter-intuitive, but generally the less your fork or shock moves as a result of a bump, the faster the shaft moves. The more the suspension moves, the slower the shaft moves.

    Friction primarily is felt in high shaft speed events. Thus, kashima forks nicer on all the small choppy stuff, but you're much less likely to notice on big hits.

  4. #4
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    Btw the spring-back mentioned in the first post is controlled by rebound damping. You can actually have high and low speed rebound damping, also, but no MTB fork or shock I've owned has it.

  5. #5
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    Quote Originally Posted by mullen119 View Post
    you want to run enough to keep high shaft speed impacts feeling under control
    What does this mean?

    Usually when I do fork tuning, I like to keep turning down both the compression and rebound knobs and the fork gets more plush, but then starts to feel wallow-ey and rubbery. Where do I add the damping back in?

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    Pretty much all rear shocks have a HSR circuit and lots of forks have it as well. Not many have an external adjustment for it though.

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    Yes, I was referring to an external adjustment for it. A 4-way adjustable shock or fork would have high and low speed compression and rebound.

    Beanbag: it means that if you don't have enough damping, the fork or shock will feel like a spring, which bounces several times per hit.

    Here's what I do to tune my suspension.

    1. set sag appropriately for the trail. make sure you are fully geared up-- water, camelbak, shoes, helmet, etc. if you want a firm ride, for a relatively smooth course or to optimize pedaling, set sag to 15-20%. if you want a more plush ride, and to ensure you use more travel, set sag to 25-30%. this is pretty easy with an air fork, but you might find that with a coil you can only set so much preload if you are light for the spring.

    2. turn the knobs all the way firm until they stop. all of them. now count each click as you turn them soft. now set the knobs in the middle if you're average weight, or 1-2 clicks firmer if you are heavier. (heavier riders use more spring rate, which requires more damping). 1-2 clicks softer if you're significantly below 170.

    3. find a test section to ride. some people use stairs as a quick guideline, but I don't think it can replace the feel of 1-2 miles of trail. make sure this test section has everything you need to test-- big hits, stutter bumps, hard braking.

    4. observe travel.
    bottomed out - add compression (preferred) or air, or reduce preload. if your fork or shock lacks compression adjustment then you may have to choose between appropriate sag and not bottoming out.

    5. DO NOT CHANGE MORE THAN ONE THING AT A TIME. the biggest mistake made when tuning is to change more than one setting at a time. you can easily get confused about what knob is responsible for what you like/dislike about the ride quality.

    6. test ride again and observe ride quality differences and travel. do this as much as you need to dial in your balance of bump absorption and travel.

    7. now pay attention to how the bike handles after landing a big jump and over little bumps. if it springs back too fast, add rebound damping. don't add too much or the suspension will wallow-- it won't return to neutral in time for the next bump.

    8. while it is fresh in your mind, write down (on paper or your smartphone) what your settings are and what trail you set them on. this is the second big mistake people make-- not writing down a known good setting, or if your tuning is incomplete, write down what you have so far and what you need to tune next. write down notes about how much travel you used, air pressure (or preload), and how many clicks on each knob.

    what are you tuning for-- what's the "right" final setting?
    obviously a lot of this is going to be personal preference. some people like the pedaling and handling of a stiffer suspension. others want maximum plushness, which works especially well if you have no drops or jumps on the trail. and a few like fast rebound, but I can't figure why.

    hope this helps!

  8. #8
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    Quote Originally Posted by ColinL View Post
    hope this helps!
    Thank you for taking the time to type that out. It DOES help.

    (a former Kansan, now transplanted to Maine)

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    Quote Originally Posted by ColinL View Post
    Yes, I was referring to an external adjustment for it. A 4-way adjustable shock or fork would have high and low speed compression and rebound.
    If it had HSR adjustment it would more than likely be a 5 way since preload adjustment is probably the most common adjustment any shock or fork has for any sport. Not trying to knit pick your post.

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    Thanks for the guide, but the knobs only influence low speed damping. I have the ability to take apart the damper and shuffle shims around.

  11. #11
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    Quote Originally Posted by beanbag View Post
    Thanks for the guide, but the knobs only influence low speed damping. I have the ability to take apart the damper and shuffle shims around.
    What fork do you have? A Manitou?

    What ride characteristics are you looking for?

  12. #12
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    minute pro

    plush and shock absorbing, with just enough platform until it starts affecting bump sensitivity.

    Actually, never mind what I want. Look back at post 5 and tell me what you think.

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    Looked at post 5. Instead of going through all the 8 steps I posted, let's shorten it a bit:

    If your sag is good, you need more compression and rebound damping. I would start with rebound, to see if maybe that's all you lack. Don't change them both at the same time. As you add compression, you will naturally lose some plushness. That's how it goes.

    If your sag isn't good, then do the whole enchilada.

  14. #14
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    Quote Originally Posted by kan3 View Post
    If it had HSR adjustment it would more than likely be a 5 way since preload adjustment is probably the most common adjustment any shock or fork has for any sport. Not trying to knit pick your post.
    For coils, sure. Air forks and shocks do not have preload. But yes, you're right, and long-travel coil is likely to be 5-way.

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    The never ending quest for Low Speed and High Speed damping force characteristics! Something we chase every day!

    The biggest problem I see with the understanding of how much and when for home tuners, and even a lot of suspension tuning companies, is that it takes a lot of equipment to actually understand what the fork or shock is doing.

    First part of the equation is understanding what the fork is doing during a specific event. For instance, when you hit the brakes at 15mph at what velocity is the fork moving. When you run over successive roots, when you run over successive roots during braking, when you hit a curb, etc. Without this information it's very hard to know what to change. This is where on-board data logging comes into play. Data loggers allow you to see the event and give you an understanding of the amount of travel, the velocities involved, and the amount of g-load being generated to better understand how much the chassis is moving(harshness).

    Armed with that information, you can then run the fork or shock on a suspension dyno to measure the amount of forces being generated. Make adjustments, re-run on the dyno to verify that you changed the point in the force curve that you meant to change, and then get back out on the trail. Rinse and repeat, and eventually you end up with the best overall compromise.

    I've attached a few screenshots from our data logging units and suspension dyno for your viewing pleasure.

    One note I will mention is that too broad of a range adjustable externally is generally not a great thing, except in the area of designs such as the CCDB. Generally speaking if you're getting a broad range externally than your force curve is too linear and is leaning to much towards a single port, or port orifice, damping system. This is great with out of the box suspension components, as the manufacture doesn't know who the end user will be, but not great for those experimenting and tuning at home. If your shimmed system is working efficiently, the external adjusters are generally controlling a small window of the force curve.

    Darren
    Attached Thumbnails Attached Thumbnails Can somebody explain high speed damping? (on forks)-travel-bottoming.jpg  

    Can somebody explain high speed damping? (on forks)-velocity.jpg  

    Can somebody explain high speed damping? (on forks)-dyno.jpg  


  16. #16
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    The fact you guys own a shock dyno and know how to use it certainly make me more likely to consider your tuning services.

  17. #17
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    Quote Originally Posted by beanbag View Post
    minute pro

    plush and shock absorbing, with just enough platform until it starts affecting bump sensitivity.

    Actually, never mind what I want. Look back at post 5 and tell me what you think.
    One thing to keep in mind is that there is a huge crossover between LSC and HSC adjustments. For example, if you use an extremely stiff HSC shim stack and keep the LSC fully open, the fork will still flow enough oil to feel pretty smooth overall. Same for the opposite. A weak shim stack with LSC full closed will still flow enough oil to allow the fork to move with fairly low restriction. This is something that is worse with damper designs like ABS+ and Mission Control. When tuning the fork, its best to keep in mind what setting you are likely to run your LSC at when picking a shim stack.

    Also, HSC events can happen on impacts that use any amount of travel. Jumps to transitions do tend to be more of a LSC event, while jumps to flat and drops to flat tend to be HSC events. Small bumps can also be either high or low speed events, mainly decided on the shape of the bump(square edged bumps tend to be HSC events and smaller rounded bumps and dips in the trails are LSC.


    As for what I meant by feeling under control. The best way I can describe it is to say you want the fork to feel that it uses the perfect amount of travel for any given compression. So if you land a jump and if feels like it spikes , then I would feel like there is too much compression and the fork should have used a little more travel to absorb the impact. If on the same jump, I feel like it blew through the travel and was diving, I would feel like I needed a little more. This is where having the proper spring rate is the first thing to set up and the most important. You dont want to confuse a diving fork as not enough damping when in fact its under sprung. Spring rate trumps all. damping is like fine tuning.

    Now the ABS+ damper, although slightly flawed by the cross over problem, is great for custom tuning and still one of the best fork dampers on the market. The reason is the dished piston. You have 3 choices for tuning. A highly preloaded shim stack that when the LSC is closed, gives a firm platform(generally for XC). A slightly preloaded shim stack that gives a slight platform(AM). Or no preload and no platform. (more for DH)
    Which style you choose depends on what you want. It sounds like you are looking for the middle ground AM style stack. As for which stack you choose, that depends on where you want to run your LSC. Thats why the dyno charts are so great. It really narrows the search for you.

    Hope that helps

    Edit: I'm glad darren chimed in. All of what I wrote is based off my personal experience which is extremely limited in comparison to his. If any of what I wrote is wrong, feel free to correct me Darren, Im still learning like most of us.

  18. #18
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    Quote Originally Posted by PUSHIND View Post
    The never ending quest for Low Speed and High Speed damping force characteristics! Something we chase every day!

    The biggest problem I see with the understanding of how much and when for home tuners, and even a lot of suspension tuning companies, is that it takes a lot of equipment to actually understand what the fork or shock is doing.

    First part of the equation is understanding what the fork is doing during a specific event. For instance, when you hit the brakes at 15mph at what velocity is the fork moving. When you run over successive roots, when you run over successive roots during braking, when you hit a curb, etc. Without this information it's very hard to know what to change. This is where on-board data logging comes into play. Data loggers allow you to see the event and give you an understanding of the amount of travel, the velocities involved, and the amount of g-load being generated to better understand how much the chassis is moving(harshness).

    Armed with that information, you can then run the fork or shock on a suspension dyno to measure the amount of forces being generated. Make adjustments, re-run on the dyno to verify that you changed the point in the force curve that you meant to change, and then get back out on the trail. Rinse and repeat, and eventually you end up with the best overall compromise.

    I've attached a few screenshots from our data logging units and suspension dyno for your viewing pleasure.

    One note I will mention is that too broad of a range adjustable externally is generally not a great thing, except in the area of designs such as the CCDB. Generally speaking if you're getting a broad range externally than your force curve is too linear and is leaning to much towards a single port, or port orifice, damping system. This is great with out of the box suspension components, as the manufacture doesn't know who the end user will be, but not great for those experimenting and tuning at home. If your shimmed system is working efficiently, the external adjusters are generally controlling a small window of the force curve.

    Darren
    I wish I could afford all that tech Trial and error is such a pain in the a$$.

  19. #19
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    As a visual, this is a link from the Roehrig website, kind of offers a visual into some of this discussion.

    http://www.roehrigengineering.com/Do...ear_shock2.wmv



    Related to the graphs posted by PUSH, Darren, one item I have never been able to grasp from tuners that do utilize data logging such as a Shock Clock and a Dyno, why is it that when data logs record events, the events reach values easily well above the dynos capability, how can the information be compared or valid?

    I ask, using your posted information, based on peak recorded compression events of over 2ms or approximately 80 inches per second, yet your dyno run sheet maxes out at 10 IPS illustrated with what appears to be a possible 22 IPS not selected. Granted these may not be related dampers or runs.

    Just curious how the difference between data logged at high IPS values can be compared to testing / building dampers at low IPS values.

    I am likely wrong but was taught that to properly evaluate and utilize the equipment, the dyno needed to have a capability to match the recorded events of the Shock Clock. Dyno testing at low IPS works well for smooth terrain, like pavement, but even Roehrig recommends seriously high IPS for off-road applications.

    Not bashing your equipment or what results you achieve, just curious how other shops and your shop validate or tune true HSC events on the dyno.

    PK
    Attached Thumbnails Attached Thumbnails Can somebody explain high speed damping? (on forks)-velocity.jpg  

    Can somebody explain high speed damping? (on forks)-dyno.jpg  

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  20. #20
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    Related to the graphs posted by PUSH, Darren, one item I have never been able to grasp from tuners that do utilize data logging such as a Shock Clock and a Dyno, why is it that when data logs record events, the events reach values easily well above the dynos capability, how can the information be compared or valid?

    I ask, using your posted information, based on peak recorded compression events of over 2ms or approximately 80 inches per second, yet your dyno run sheet maxes out at 10 IPS illustrated with what appears to be a possible 22 IPS not selected. Granted these may not be related dampers or runs.

    Just curious how the difference between data logged at high IPS values can be compared to testing / building dampers at low IPS values.

    I am likely wrong but was taught that to properly evaluate and utilize the equipment, the dyno needed to have a capability to match the recorded events of the Shock Clock. Dyno testing at low IPS works well for smooth terrain, like pavement, but even Roehrig recommends seriously high IPS for off-road applications.

    Not bashing your equipment or what results you achieve, just curious how other shops and your shop validate or tune true HSC events on the dyno.
    You are correct in the fact that the data I provided is from two different items. The data logging from a Lyrik fork, and the dyno info from a CRF250 Showa rear shock. As I mentioned, we spend a lot of money on this stuff...don't want to give up the recipe for free!

    As for your comments regarding equipment, I do disagree with your velocity ranges as our Roehrig crank dyno is capable of 1m/sec. A lot of damper tuning is done under that range. what you're referring to are "peak events" and that most of the average peaks fall near this range of the crank dyno. Again, not wanting to give out too much velocity info.

    That being said, we did ante up and purchase a Roehrig Engineering EMA dyno. This machine allows us the opportunity to create multiple wave forms and simulate actual bumps imported directly from our on-board data logging. This was a massive investment to further our research so that we could start to better understand the upper limitations of our piston and valve designs. We're looking into filming a serious of technical videos for the web and one of the things we're going to touch on is this subject. This will help put all of this into perspective.

    We take our engineering quite serious. PMK, with our engineering resources and our state-of-the-art CNC machining facility, and our technical services department, I can assure you that it would be like a day at Disneyland for someone like you if you were to come visit! You're welcome anytime...and that goes out to anyone!

    Darren

  21. #21
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    Thanks for the suggestions, mullen. I don't think I ever come close to bottoming my fork during normal riding, even though I can easily bottom it by bouncing the bike on purpose. I guess that's just my riding style to not ram into things. So with that said, it would seem like I don't need a whole lot of high speed compression. One lower bound that I can think of for the high speed compression damping is that it has to at least damp the unsprung weight of the wheel and fork lowers. That calculates out to [something I will figure out later].

    I'm not sure what I will gain from the datalogging. How will it tell me where more or less damping is needed? Do I get to do a Rouelle histogram analysis? (This reminds me that there is a lot of research done on this in the FSAE and professional motorsports community)

    Also, you are right that the adjuster knob on the ABS+ dampers affects damping way out to high speeds. Must be that speed shim. That being the case, one good suggestion I ran across was from some link to an article in Decline magazine that showed up in the ABS+ tunign thread. It goes something like:

    ride around and adjust the damper for best cornering and braking response. Note the damping force at 30cm/s according to the chart. (No dyno needed)

    Ride a bumpy section and adjust the damper for best performance / comfort. Note the value at 120cm/s.

    Find a shimstack that give you this curve without using the adjuster.

    Manitou ABS+ Tune kit Decline March 2012

    I have both a dynometer and a data-logger, but there isn't much point if they can't give me actionable recommendations.

  22. #22
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    Also, my ghetto hand dyno built out of unistrut and aluminum scraps can do 50 ips and arbitrary waveforms too.

    Last edited by beanbag; 11-02-2012 at 06:52 AM.

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    I'm not sure what I will gain from the datalogging. How will it tell me where more or less damping is needed? Do I get to do a Rouelle histogram analysis? (This reminds me that there is a lot of research done on this in the FSAE and professional motorsports community)
    Just looking at one common example....the question of "my suspension feels too stiff". This could because you're not getting enough travel for a given bump, or because you're using too much travel and excessively preloading the springs. The data would obviously tell you this. You ould then make adjustments, and create a histogram to evaluate the changes in combination with your notes on ride "feel".

    Also, you are right that the adjuster knob on the ABS+ dampers affects damping way out to high speeds. Must be that speed shim. That being the case, one good suggestion I ran across was from some link to an article in Decline magazine that showed up in the ABS+ tunign thread. It goes something like:

    ride around and adjust the damper for best cornering and braking response. Note the damping force at 30cm/s according to the chart. (No dyno needed)

    Ride a bumpy section and adjust the damper for best performance / comfort. Note the value at 120cm/s.
    Agreed, if you're using the external adjustments to control the peak events, than you're most likely making large compromises to the overall ride quality.

    I have both a dynometer and a data-logger, but there isn't much point if they can't give me actionable recommendations.
    I'm confused, because if you have this equipment you must already know what velocities fall under low speed and what events fall under high speed and can tune accordingly. Your original post is asking "Can somebody explain high speed damping? (on forks)"

    Also, my ghetto hand dyno built out of unistrut and aluminum scraps can do 50 ips and arbitrary waveforms too
    Pretty trick! It appears that you have to pull the arm to actuate the fork? How come you didn't go with a setup that would allow you to push(no pun intended) on it to make it easier on your back?

    Darren

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    I really like you homemade dyno. Its pretty slick. On the other hand, I am somewhat confused as to why you need a dyno for a fork with the TK damper

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    Ok, so which company is going to build me a digital fork that after a ride I can connect to my laptop and get a readout and retune the specs... All for under $500....


  26. #26
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    Quote Originally Posted by PUSHIND View Post
    You are correct in the fact that the data I provided is from two different items. The data logging from a Lyrik fork, and the dyno info from a CRF250 Showa rear shock. As I mentioned, we spend a lot of money on this stuff...don't want to give up the recipe for free!

    As for your comments regarding equipment, I do disagree with your velocity ranges as our Roehrig crank dyno is capable of 1m/sec. A lot of damper tuning is done under that range. what you're referring to are "peak events" and that most of the average peaks fall near this range of the crank dyno. Again, not wanting to give out too much velocity info.

    That being said, we did ante up and purchase a Roehrig Engineering EMA dyno. This machine allows us the opportunity to create multiple wave forms and simulate actual bumps imported directly from our on-board data logging. This was a massive investment to further our research so that we could start to better understand the upper limitations of our piston and valve designs. We're looking into filming a serious of technical videos for the web and one of the things we're going to touch on is this subject. This will help put all of this into perspective.

    We take our engineering quite serious. PMK, with our engineering resources and our state-of-the-art CNC machining facility, and our technical services department, I can assure you that it would be like a day at Disneyland for someone like you if you were to come visit! You're welcome anytime...and that goes out to anyone!

    Darren
    Good answer. The best way to evaluate HSC events is to buy a bigger dyno. The adapter / rate changer method is something I have heard of others fabricating. Basically trying to emulate higher IPS at the peak HP output of the dyno power supply.

    You will enjoy that EMA dyno and no doubt expand your capabilities.

    It has been about 10 years since I shopped for a dyno. This was the era when the shock clock and EMA units seemed to be just arriving. It was pretty cool to realize that with enough money you could data log, then go pretty much right into the dyno with the exact data logged run.

    PK
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  27. #27
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    Quote Originally Posted by PUSHIND View Post
    Just looking at one common example....the question of "my suspension feels too stiff". This could because you're not getting enough travel for a given bump, or because you're using too much travel and excessively preloading the springs. The data would obviously tell you this. You ould then make adjustments, and create a histogram to evaluate the changes in combination with your notes on ride "feel".
    I've never heard of using "too much travel". What would it look like in the data? If I combine the velocity and position data with the dyno data to get a plot of forces, I can only find justifications for reducing the compression damping at certain point. Where can I find rationale for adding more damping?

    I'm confused, because if you have this equipment you must already know what velocities fall under low speed and what events fall under high speed and can tune accordingly. Your original post is asking "Can somebody explain high speed damping? (on forks)"
    I only used the data logger setup on the car and not the bike yet. It was mainly used to find some peak velocities and confirm what are the shaft speeds for body rolling motions. On the Bilstein shocks I worked on, there was a clear transition between the bleed and shim portion. Other than that, I did not figure out from the data where to add more or less damping. I ended up tuning by feel and a few mathematical rules related to critical damping.

    How come you didn't go with a setup that would allow you to push(no pun intended) on it to make it easier on your back?
    Because usually rebound damping forces are higher, and that is achieved by pushing on the lever. But I mainly had it this way coz it lets stuff stick up above the shock.
    Last edited by beanbag; 11-02-2012 at 03:57 PM.

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    Too much travel would manifest itself at some point as excessive brake dive and/or bottoming out.

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    It has been about 10 years since I shopped for a dyno. This was the era when the shock clock and EMA units seemed to be just arriving. It was pretty cool to realize that with enough money you could data log, then go pretty much right into the dyno with the exact data logged run.
    Yeah, we're over six figures deep with our new setup which is pretty scary!

    I've never heard of using "too much travel". What would it look like in the data? If I combine the velocity and position data with the dyno data to get a plot of forces, I can only find justifications for reducing the compression damping at certain point. Where can I find rationale for adding more damping?
    I was speaking in reference to a specific situation.

    Rider A 175lbs running 75psi of air pressure in a 140mm fork is complaining of harshness in their suspension. Data logging shows that for a specific section of trail we expect to see an average travel being used of 45mm with that application. In fact this rider is only seeing 21mm of average travel even though their spring rate is correct. In this scenario the compression damping is too great, or curve too steep, to allow the wheel to get effective "through travel".

    Rider B 175lbs running 75psi of air pressure in a 140mm fork is complaining of harshness in their suspension. Data logging shows that for a specific section of trail we expect to see an average travel being used of 45mm with that application. In fact this rider is only seeing 70mm of average travel even though their spring rate is correct. In this scenario the compression damping is too soft, or curve to shallow, allowing the wheel to move too easily through the travel allowing sharp accelerations and building up more spring load causing excess firmness.

    Darren

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    Quote Originally Posted by PUSHIND View Post
    Yeah, we're over six figures deep with our new setup which is pretty scary!
    Darren

    @ Darren...Understand 100%, that was my turning point in suspension. Take it to the next level, or enjoy my aerospace career with good pay, benefits and less headaches. With no regrets, I prefer high end aerospace over suspension.

    Did you buy a new EMA from Roehrig or purchase the used one I saw listed on the internet that was low time and about a year or slightly more old?

    I'm assuming you purchased a sister unit to the one JGR has. In my opinion that is the capability required, I just am not sure the bicycle components structurally can handle those repeated tests / loads without silly failures. Anything with snaprings or plastic based sealheads would be in question.



    @Beanbag / OP, sorry for the derail. The others have posted good info to guide you. To keep it simple, in regards to HSR, this shim setting requires the ability to take a deep stroke extension and control but also smoothly blend the high compressed spring force into a low spring force.

    Getting more technical...So basically, this works the firmer portion of the shims (but in reality all shims and freebleed port) to control extension speed while tapering onto the less firm portion of the shims and ultimately only the freebleed (not 100% freebleed but close). In riding, you expect rebound extension to not hold the wheel packed or compressed nor allow it to bounce. Sadly, most bicycle riders overlook that proper rebound is also a respectable aid in how a bike turns and holds a line through a corner. A fast rebound will make the bike run wide in corners, while a slow rebound can contribute to "tuck" or with soft terrain knifing. Ultimately, this also directly relates to the forks geometric trail dimension, dynamic trail dimension, dynamic headtube angle, and fork offset.

    As for your HSC true question. The compression control can become more complex than the rebound. Here's why. Compression is not controlled by a finite force of the spring. Compression forces are dependent upon many factors. Some would be obvious rider weight, style and terrain. More complex though are headtube angle, sag, fork tube overlap, stiction, spring drag / air seal drag, damper shaft to cartridge body ratio, valve body area, valve body to shim fulcrum distance, piston edge effect and then the more typical and easy stuff such as shim stack formats, oil viscosity.

    In a nut shell, the goal of HSC, is to provide a somewhat platform situation but not really getting the job done. The forks freebleed will allow the fork to dive or wallow if open excessively. So in many senses, the freebleed (LSC adjuster) often is more of a pressure limiting orifice to control cartridge peak pressure in an open style cartridge system. In a closed cartridge system, the function is similar, however the control is not against the open chamber but against the cartridges pressure function IFP, bladder etc.

    LSC must be set so the shims and freebleed find that equilibrium of no wallow or dive, and yet be able to assist in tuning cartridge pressure dumping. Ideally, another circuit known as a midvalve will be employed. The typical LSC is by static shimming, while a midvalve is a dynamic shim set on the opposite side of the piston from the rebound shims. The MV is able to pick up the deficiency of the LSC shims, and offer the proper mid travel support, thereby controlling dive and getting better transitions into the deep portion of travel. Sad part about a midvalve is that often the cartridge shaft to cartridge bore ratio is poor, can not be tuned, and forces compromises on MV settings. Also, in many situations, the optimum MV settings are not ones that provide long MV shim life.

    HSC, is a form where in rapid suspension compression, while all circuits combined give total HSC values, in theory, the LSC, and MV phase out, leaving only the firmer portion of the static shims (actually all static shims combined) and the ability of the freebleed to control but dump cartridge pressure. This rapid movement creates rapid fluid flows which can be felt as spikes. They can occur at both high and low vehicle speeds. The typical term used when testing for HSC settings is a square edged bump (root).

    The earlier items mentioned, especially fork overlap and geometry play big on this as mechanical binding is very commonly confused for HSC.

    Tuning HSC ca provide a challenge. I agree with Darrens approach of the dyno in HSC testing, provided the numbers are real world. Unfortunately, the dyno is truly linear in motion and most times will not see mechanical issues. Therefore, when setting HSC, it is best to test sections of terrain that have the fork well compressed, typically about 50%. This lessens the forks length / leverage and binding. Under these conditions, normally it under braking into chop / hack. You need to focus on if the hands feel true spikes or smooth increase from added spring compression. Then make a change, easiest is opening the LSC, and note how it feels in the same conditions ( yes it may bob more during approach), but is there less harshness? Try adding compression until harshness is felt. This will offer insight into how to alter the static shim stack. Often the easiest change is an adjustment to the clamping shim diameter. Other shims may require changes also, but the clamp is a good start.

    As for how these conditions plot on a dyno, all transition should be smooth. In regards to the slope for HSC, you are dealing with preferences of each individual rider, so this will vary the requirements seen by the dyno, and the degree of slope plotted. In a nutshell, no two riders are the same, so in theory, each riders ideal setting will be different when plotted by a dyno. The dyno can ensure that multiple sets of suspension perform similar for a given rider. The dyno can help pinpoint mechanical concerns such as port area concerns, shaft / body ratio issues, or large errors in shim selection. In the end, the best dyno setting still require someone to ride them.

    Not sure if this helped or just rambled.

    PK
    Last edited by PMK; 11-03-2012 at 04:34 AM.
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    Data loggers and dyno's are great but the high speed recording modes on some of the newer cameras are also a great tool, particularly for evaluating tyre + suspension performance. Being able to step through some 240fps footage allows you to quickly determine which of the two compression issues Darren was talking about. Corner entry and exit footage can also allow you to see what you're rebound is doing. For shorter suspension travel in the 100-120mm range, the suspension effect of large volume tyres plays a big part in the overall package, to the tune of adding 20-40mm of extra "travel". The camera helps see how the tyre and suspension interact.

    I've got a small Canon that has frame by frame playback in the camera so all of this can be done with a couple of people trailside.

    Grab a mate, grab a camera and get some footage.

  32. #32
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    Quote Originally Posted by TigWorld View Post
    Data loggers and dyno's are great but the high speed recording modes on some of the newer cameras are also a great tool, particularly for evaluating tyre + suspension performance. Being able to step through some 240fps footage allows you to quickly determine which of the two compression issues Darren was talking about. Corner entry and exit footage can also allow you to see what you're rebound is doing. For shorter suspension travel in the 100-120mm range, the suspension effect of large volume tyres plays a big part in the overall package, to the tune of adding 20-40mm of extra "travel". The camera helps see how the tyre and suspension interact.

    I've got a small Canon that has frame by frame playback in the camera so all of this can be done with a couple of people trailside.

    Grab a mate, grab a camera and get some footage.
    100% correct, riders can't lie when video proof is there.

    FWIW, It is a known fact that when I test with riders and accomplish best settings for an individual, whether moto or MTB, I listen intently on what is said from the riders perspective, see how their comments compare to what I watched. If the rider makes his own suggestions on what clicker to "click", I will agree, and make my own adjustments. Send them back out and again get their feedback and compare to what I watched. A good majority of the time, what the rider feels is valid but the change in settings wanted is incorrect.

    The obvious question from me upon their return from a short hot lap "is it better?". Most riders are setback slightly to realize when I explain the exact change and why I made the change, that their choice would be a move in the wrong direction.

    Most common complaint is in regards to a forks HSC, especially under braking with hack. Many times this is resolved with a rear shock setting change, crazy but true where we ride. The rear may not track properly or could be pitching around the front axle. Settle the rear, the rider is more confident and riding relaxed, which settles the chassis further, allowing suspension to work, resolving the apparent HSC issue. Crazy but often happens. As an added benefit, corner speed is also increased.

    Again, the camera does not lie.

    PK
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    Ok, so which company is going to build me a digital fork that after a ride I can connect to my laptop and get a readout and retune the specs... All for under $500....
    I wish! We's sell a ton of those!

    Did you buy a new EMA from Roehrig or purchase the used one I saw listed on the internet that was low time and about a year or slightly more old?

    I'm assuming you purchased a sister unit to the one JGR has. In my opinion that is the capability required, I just am not sure the bicycle components structurally can handle those repeated tests / loads without silly failures. Anything with snaprings or plastic based sealheads would be in question.
    The dyno on the web that you're refering to is owned by ling time buddy of mine Dave Weagle. Initially, we were going to buy that one and trade our crank dyno to him as part of the deal. Long story short, we chose to keep the crank dyno for our technical services department to use and have the EMA for engineering. Dave's unit is very well configured, but because of our dual use for both MTB and Moto, we ultimately went direct and had Roehrig build us a custom unit configured for our specific needs.

    Data loggers and dyno's are great but the high speed recording modes on some of the newer cameras are also a great tool, particularly for evaluating tyre + suspension performance. Being able to step through some 240fps footage allows you to quickly determine which of the two compression issues Darren was talking about. Corner entry and exit footage can also allow you to see what you're rebound is doing. For shorter suspension travel in the 100-120mm range, the suspension effect of large volume tyres plays a big part in the overall package, to the tune of adding 20-40mm of extra "travel". The camera helps see how the tyre and suspension interact.

    I've got a small Canon that has frame by frame playback in the camera so all of this can be done with a couple of people trailside.
    Yeah, we have hundreds of hours of HS camera footage that we use in conjunction with all of our other toys. It does act as a very useful track/trailside tool. Again, when used in conjunction with other items, you can get a pretty good look at what's going on. Our youtube channel is pretty lame at this point, but here's a clip that's been up there for a while. We shoot between 420-1000f/s depending on the application.

    <iframe width="560" height="315" src="http://www.youtube.com/embed/odGDEa4TeJY?list=UUprHyRc4tmkQ918Bjx01ksA&amp;hl=e n_US" frameborder="0" allowfullscreen></iframe>

  34. #34
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    Quote Originally Posted by PMK View Post
    Related to the graphs posted by PUSH, Darren, one item I have never been able to grasp from tuners that do utilize data logging such as a Shock Clock and a Dyno, why is it that when data logs record events, the events reach values easily well above the dynos capability, how can the information be compared or valid?

    I ask, using your posted information, based on peak recorded compression events of over 2ms or approximately 80 inches per second, yet your dyno run sheet maxes out at 10 IPS illustrated with what appears to be a possible 22 IPS not selected. Granted these may not be related dampers or runs.

    Just curious how the difference between data logged at high IPS values can be compared to testing / building dampers at low IPS values.

    I am likely wrong but was taught that to properly evaluate and utilize the equipment, the dyno needed to have a capability to match the recorded events of the Shock Clock. Dyno testing at low IPS works well for smooth terrain, like pavement, but even Roehrig recommends seriously high IPS for off-road applications.

    Not bashing your equipment or what results you achieve, just curious how other shops and your shop validate or tune true HSC events on the dyno.

    PK
    Having that kind of dyno capability is more important for anyone creating new valve geometry than someone simply retuning an existing damper, because when working with an existing piston, one has to simply deal with its flow capacity characteristic on the assumption that it is capable of allowing enough oil flow at the peak velocities. The reason for this is that the vast majority of critical motions (with respect to both stability and harshness) occur at only a fraction of the highest peak velocities (have personally logged velocities substantially higher than shown in those graphs, and the ShockClock has a very low sample rate as it is). I certainly don't want to speak for other tuners, but building new pistons for existing dampers (if they are well developed dampers with no known tendency to spike at peak velocities) allows one the luxury of simply matching or exceeding the HS port area of the stock piston in order to assume that the velocity ceiling of the new valve is at least as high as the old one.

    How this is relevant: The geometry of shimmed valves typically lends itself to surprisingly linear high speed F-V curves up until the actual port geometry becomes the limiting factor in terms of flow (quite low in rebound, very high in compression), because the distances shims actually bend are surprisingly tiny within their linear range of motion (for example, shim displacement at its OD may be as little as 0.1mm at 0.5m/s in certain dampers). Most progression or digression, for example, is little to do with the specific port geometry and largely to do with the transition characteristics between the LS and the HS circuits.

    A capable engineer can get a good estimation of the choking velocities of the HS porting just through calibrated measurements alone, which allows for some degree of extrapolation of the HSC curve - a curve that is linear from 0.1m/s to 1m/s is not going to suddenly and violently change by 1.1m/s, for example, but may have a distinct change in its gradient by 2m/s. The bigger the ports and the stiffer the valving, the further the extrapolations are valid, though these need to be calibrated through both calculation and measurement. This extrapolation can be a somewhat imprecise science, but it can be implicitly confirmed by further datalogging with known port geometry, and is something that is observable and measurable with certain high end shocks that are already on the market (particularly in rebound), even well under the 1m/s limit of the Roehrig crank dyno that we have.

    However, it should be noted that the majority (not the entirety, but the majority) of good tuning doesn't come from the super complex mathematical analyses, but from fundamental measurements such as comparative travel usage, statistical analysis of position and velocity measurements, derived accelerations etc. The ShockClock, despite its many limitations as a datalogger, gives a pretty good idea of a lot of that stuff.
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    Having that kind of dyno capability is more important for anyone creating new valve geometry than someone simply retuning an existing damper, because when working with an existing piston, one has to simply deal with its flow capacity characteristic on the assumption that it is capable of allowing enough oil flow at the peak velocities. The reason for this is that the vast majority of critical motions (with respect to both stability and harshness) occur at only a fraction of the highest peak velocities (have personally logged velocities substantially higher than shown in those graphs, and the ShockClock has a very low sample rate as it is). I certainly don't want to speak for other tuners, but building new pistons for existing dampers (if they are well developed dampers with no known tendency to spike at peak velocities) allows one the luxury of simply matching or exceeding the HS port area of the stock piston in order to assume that the velocity ceiling of the new valve is at least as high as the old one.

    How this is relevant: The geometry of shimmed valves typically lends itself to surprisingly linear high speed F-V curves up until the actual port geometry becomes the limiting factor in terms of flow (quite low in rebound, very high in compression), because the distances shims actually bend are surprisingly tiny within their linear range of motion (for example, shim displacement at its OD may be as little as 0.1mm at 0.5m/s in certain dampers). Most progression or digression, for example, is little to do with the specific port geometry and largely to do with the transition characteristics between the LS and the HS circuits.

    A capable engineer can get a good estimation of the choking velocities of the HS porting just through calibrated measurements alone, which allows for some degree of extrapolation of the HSC curve - a curve that is linear from 0.1m/s to 1m/s is not going to suddenly and violently change by 1.1m/s, for example, but may have a distinct change in its gradient by 2m/s. The bigger the ports and the stiffer the valving, the further the extrapolations are valid, though these need to be calibrated through both calculation and measurement. This extrapolation can be a somewhat imprecise science, but it can be implicitly confirmed by further datalogging with known port geometry, and is something that is observable and measurable with certain high end shocks that are already on the market (particularly in rebound), even well under the 1m/s limit of the Roehrig crank dyno that we have.

    However, it should be noted that the majority (not the entirety, but the majority) of good tuning doesn't come from the super complex mathematical analyses, but from fundamental measurements such as comparative travel usage, statistical analysis of position and velocity measurements, derived accelerations etc. The ShockClock, despite its many limitations as a datalogger, gives a pretty good idea of a lot of that stuff.
    Steve, are you the Steve originally from Oz? Anyway, I checked out your site....looks like you've got some cool stuff going on.

    Darren

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    Quote Originally Posted by PUSHIND View Post
    Steve, are you the Steve originally from Oz? Anyway, I checked out your site....looks like you've got some cool stuff going on.

    Darren
    I am indeed, thank you, and likewise. How did you know I am from Australia?

    Steve
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    I am indeed, thank you, and likewise. How did you know I am from Australia?
    Because I know all things suspension tuning! LOL

    Actually you came up in a conversation recently with a colleague and I seemed to remember having some email conversations with you via rotorburn or something trying to coordinate maybe a test sample or something. Anyway, just putting two and two together, but still had to ask to confirm.

    Darren

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    Steve, I read your post quickly. I don't disagree. I would add though that sometimes on poorly designed pistons or valve bodies, sometimes changes can be easily made to see large gains.

    As an example, White Power forks used on KTMs have had valve body design concerns. DIY / home tuners have followed advice of others and made simple changes obtaining excellent results with simple tools such as a Dremel to "port" the valve body. This is a good example of F-V concerns from the oem.

    One concept often overlooked, is flow based on damper shaft to body bore ratio. From experience, each ratio tends to lend itself to different port area percentage values. Add to this edge effect, port shape, and fulcrum distance the net design is sometimes not an easy target.

    Obviously there must be a need to replace or modify the valve body. Sometimes you can have too much flow capability.

    PK
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    Quote Originally Posted by PUSHIND View Post

    Rider B 175lbs running 75psi of air pressure in a 140mm fork is complaining of harshness in their suspension. Data logging shows that for a specific section of trail we expect to see an average travel being used of 45mm with that application. In fact this rider is only seeing 70mm of average travel even though their spring rate is correct. In this scenario the compression damping is too soft, or curve to shallow, allowing the wheel to move too easily through the travel allowing sharp accelerations and building up more spring load causing excess firmness.

    Darren
    Please explain this scenario some more. How did you know that a section of trail is "supposed" to only use 45mm of travel? How can 70mm of travel be too much? Don't you want to use as much travel as possible to best follow the terrain?

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    Quote Originally Posted by PUSHIND View Post
    Because I know all things suspension tuning! LOL

    Actually you came up in a conversation recently with a colleague and I seemed to remember having some email conversations with you via rotorburn or something trying to coordinate maybe a test sample or something. Anyway, just putting two and two together, but still had to ask to confirm.

    Darren
    Oh right, that was a while ago! If you're ever up in Whistler, give me a yell, would be nice to put a face to the name

    Quote Originally Posted by PMK View Post
    Steve, I read your post quickly. I don't disagree. I would add though that sometimes on poorly designed pistons or valve bodies, sometimes changes can be easily made to see large gains.

    As an example, White Power forks used on KTMs have had valve body design concerns. DIY / home tuners have followed advice of others and made simple changes obtaining excellent results with simple tools such as a Dremel to "port" the valve body. This is a good example of F-V concerns from the oem.

    One concept often overlooked, is flow based on damper shaft to body bore ratio. From experience, each ratio tends to lend itself to different port area percentage values. Add to this edge effect, port shape, and fulcrum distance the net design is sometimes not an easy target.

    Obviously there must be a need to replace or modify the valve body. Sometimes you can have too much flow capability.

    PK
    Agreed - some moto dampers use HS throttling ports within the pistons, where the smallest cross section is not the same as the port area sealed by the shim stacks. These are intended to provide a severe ramp up (spike/hydraulic lock, essentially) in damping at SUPER high speeds (like when you overshoot a 100ft stepdown to flat) where the HS valving has been completely overwhelmed by the momentum of the huge rigid sprung mass of the motorbike - which is far less of a concern with bicycles simply because the rider's mass (and strength) is almost always the limiting factor.

    However, if those throttling ports are too small (changes in damping force are proportional to the fourth power of the port diameter!) then that spiking will occur too severely at too low a speed. If the ports are much too large, it can be difficult to create a sufficiently stiff valving stack, flow through the LS circuit (such as the rebound adjuster) can be reduced to the point where the adjuster's effectiveness suffers severely, and other factors such as machining precision and shim tolerances become much more critical, which in turn means less precise damping control - particularly in the crucial transition region between HS and LS damping.

    Any valve design, as you say, needs to consider the mass flow rate per unit shaft speed, which is determined by the bore and shaft sizes.

    Quote Originally Posted by beanbag View Post
    Please explain this scenario some more. How did you know that a section of trail is "supposed" to only use 45mm of travel? How can 70mm of travel be too much? Don't you want to use as much travel as possible to best follow the terrain?
    Not necessarily, there are conflicting requirements on travel use:
    1. More travel use from ground-based inputs typically means less harshness and better wheel tracking. Obviously, this is good.
    2. More travel use from rider-based inputs typically means less stability, slower response and settle times, more energy dissipation (less liveliness) and in some cases (from either ground-based or rider-based inputs), higher peak forces (either from higher spring forces or bottom out). These are usually considered bad. As a result, the ideal suspension setup is one that minimises the negatives, and maximises the positives, you will never completely eliminate one issue or the other - though you may reduce negative factors into insignificance.
    Last edited by Steve VS; 11-05-2012 at 03:26 AM.
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    Just a couple questions for now:
    What does it mean when the fork has kind of a springy, rubbery feel? Where is the damping lacking?
    Is there always a trade-off between platform / brake dive resistance and some kind of small bump harshness? When I turn the compression knob back and forth, the fork seems to alternate between these conditions.

    Sometimes, I think things are exactly right. For example, when I hit a root at medium speed, the front wheel makes a "plop" sound as if the tire is flat, and there isn't much shock to the handlebars.

    Other times, even hitting a 2" rock will cause the fork to bounce off.

    Other times I hit the trailing edge of a small pothole and it is more harsh than I expect.

    For now, I took one main shim out of my ABS+ stack, which basically means the HSC is a bit lower slope and intercept.

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    Oh one other thing, regarding mullen's comment that there is a lot of "crossover" on these ABS+ dampers. I think that just means that the adjustable orifice is really big and even flows at high speeds. Contrast this with the valving design on Bilstein shocks. The bleed port is actually the first shim against the piston, but with some notches cut into it. Once you exceed a certain pressure, this shim lifts up along with all the other ones. I'm not sure if it is this aspect of the design, but it really lets the linear portion of the shims take over right after the digressive knee. On these ABS+ dampers, instead you have this big progressive / parabolic damping curve all the way up to high speeds. One thing I also learned from car suspension is that if you still have a parabolic curve into the mid-speed regions, it will feel like ass.

    Oh yeah, that's another thing that bugs me. Why do people with these high dollar dynos only plot a few points along the x axis? It totally hides the low speed behavior and crossover transition. (IMHO more important than whether your piston ports are limiting your flow at super high speeds) Wouldn't you appreciate this level of detail? For example:
    Last edited by beanbag; 11-05-2012 at 03:50 AM.

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    Quote Originally Posted by Steve VS View Post
    Oh right, that was a while ago! If you're ever up in Whistler, give me a yell, would be nice to put a face to the name



    Agreed - some moto dampers use HS throttling ports within the pistons, where the smallest cross section is not the same as the port area sealed by the shim stacks. These are intended to provide a severe ramp up (spike/hydraulic lock, essentially) in damping at SUPER high speeds (like when you overshoot a 100ft stepdown to flat) where the HS valving has been completely overwhelmed by the momentum of the huge rigid sprung mass of the motorbike - which is far less of a concern with bicycles simply because the rider's mass (and strength) is almost always the limiting factor.

    However, if those throttling ports are too small (changes in damping force are proportional to the fourth power of the port diameter!) then that spiking will occur too severely at too low a speed. If the ports are much too large, it can be difficult to create a sufficiently stiff valving stack, flow through the LS circuit (such as the rebound adjuster) can be reduced to the point where the adjuster's effectiveness suffers severely, and other factors such as machining precision and shim tolerances become much more critical, which in turn means less precise damping control - particularly in the crucial transition region between HS and LS damping.

    Any valve design, as you say, needs to consider the mass flow rate per unit shaft speed, which is determined by the bore and shaft sizes.



    Not necessarily, there are conflicting requirements on travel use:
    1. More travel use from ground-based inputs typically means less harshness and better wheel tracking. Obviously, this is good.
    2. More travel use from rider-based inputs typically means less stability, slower response and settle times, more energy dissipation (less liveliness) and in some cases, higher peak forces (either from higher spring forces or bottom out). These are usually considered bad. As a result, the ideal suspension setup is one that minimises the negatives of both, and maximises the positives, but you will never completely eliminate one or the other (though you may reduce negative factors into insignificance).

    In bold, a concept that is very often misunderstood, overlooked in design, and why many aftermarket suspension valves fail to provide anything better than a wallowy ride.

    Adding to this, the as you call them throttling ports, for those unfamiliar with them, are not the actual orifice port. The stepped throttling port has a larger net area, which more easily applies pressure onto the shim face to unseat it. In addition, the ports sealing surface, is also the derived fulcrum dimension, and when too large can make tuning via the clamp size difficult. This as mentioned, correlates to how the transition is felt by the rider as the HSC is utilized.

    Beanbag, not answering for Darren, but in laymans terms, as I read what he posted, it sounds like typical mid stroke harshness / midstroke rampup, riding low in the stroke since his example is a damping based not spring based concern. The situation can also be an overdamped setup that may have the rider opting for a softer airspring pressure on account of harshness from the shims / valving or in some cases too much bath oil causing a poor compression ratio or even a poor selection of hydraulic bottoming control. This is when it becomes very important to find the specific area creating the ride quality problem. As for the knowing it should be 45mm, that is experience and / or previous logs of what was working on another machine.

    For others reading and wondering how to resolve a HSC concern without all the data logging and dynos, build yourself a square edge style bump, or find one on the trail, that is approximately 50% of rated suspension stroke. Ensure it is secure and will not move, plus ideally is somewhat rounded on the edges. Running a high tire pressure so as to save your rim and get accurate feedback, use this as your tuning test bed that you can evaluate changes with. It is best to not pedal across it, enter exactly straight and not too fast initially. As your damping dials in, speeds with minimal feedback will increase. If your fork has a HSC adjuster, it's pretty easy to find a "best" setting for how the fork has been built within a few minutes. FWIW, on a fork like our Fox 40 on the Ventana tandem, we adjust settings while riding. The froks HSC is on top by the bars and the rear is dialed in via the old style DHX5.0 air Propedal knob. Typically we ride in certain range of the adjuster and make a click one side or the other to optimize for the terrain that day. The bike and suspension is talking to you. It's up to you to understand the language.

    Consider also, that when you send your stuff to big shops, like those posting here, you should still work the clickers to optimize the settings. There are many riders that are scared of screwing it up. Right down your initial clicker and pressure settings, then spin away on the adjusters.

    PK
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    Quote Originally Posted by PMK View Post
    The situation can also be an overdamped setup that may have the rider opting for a softer airspring pressure on account of harshness from the shims / valving

    build yourself a square edge style bump, or find one on the trail, that is approximately 50% of rated suspension stroke. Ensure it is secure and will not move, plus ideally is somewhat rounded on the edges. Running a high tire pressure so as to save your rim and get accurate feedback, use this as your tuning test bed that you can evaluate changes with. It is best to not pedal across it, enter exactly straight and not too fast initially. As your damping dials in, speeds with minimal feedback will increase.
    both good points for me to consider

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    Quote Originally Posted by PUSHIND View Post
    I wish! We's sell a ton of those!
    That would be fairly easy to do these days,especially if people are willing to hand over 500$ in retail, but I guess you already know that?



    Magura

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    Please explain this scenario some more. How did you know that a section of trail is "supposed" to only use 45mm of travel? How can 70mm of travel be too much? Don't you want to use as much travel as possible to best follow the terrain?
    Meaning that a group of test riders agree that using that much travel gives the best compromise of comfort and control.

    Oh right, that was a while ago! If you're ever up in Whistler, give me a yell, would be nice to put a face to the name
    For sure. Likewise if you're ever on Colorado you should plan on stopping by PUSH.

    Oh yeah, that's another thing that bugs me. Why do people with these high dollar dynos only plot a few points along the x axis? It totally hides the low speed behavior and crossover transition. (IMHO more important than whether your piston ports are limiting your flow at super high speeds) Wouldn't you appreciate this level of detail? For example:
    I'm actually capable of spitting out any data that you'd like. I was just showing a general graph to help visualize what I was talking about, not to actual provide exact data. You've obviously seen what dyno charts look like, but a lot of forum members have not.

    That would be fairly easy to do these days,especially if people are willing to hand over 500$ in retail, but I guess you already know that?
    Not with my current capabilities and resources! I guess we'll have to hire an electronics engineer!

    Darren
    Attached Thumbnails Attached Thumbnails Can somebody explain high speed damping? (on forks)-dyno-2.jpg  


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    Anyone know what dyno this is? These are the HSC numbers I want to know.

    <iframe width="420" height="315" src="http://www.youtube.com/embed/32XLPjdDlRA" frameborder="0" allowfullscreen></iframe>
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    Anyone know what dyno this is? These are the HSC numbers I want to know.
    That's the Roehrig EMA dyno, similar to the one we purchased recently.

    Darren

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    Quote Originally Posted by PUSHIND View Post
    That's the Roehrig EMA dyno, similar to the one we purchased recently.

    Darren
    DANG that would tell me some info! Googling away now.
    Bend, Oregon

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    I would need the 4k for the forces I need, and CRAP I don't even want to know the cost.
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    I would need the 4k for the forces I need, and CRAP I don't even want to know the cost.
    Base price on a 4k is around $100,000.....and unfortunately that's before you start configuring it for your applications. Plan on spending at least $125,000 to cover freight, setup, fixtures, etc. If you're a new customer your probably looking to fly out a Roehrig engineer for setup and training as well.

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    Quote Originally Posted by PUSHIND View Post
    Base price on a 4k is around $100,000.....and unfortunately that's before you start configuring it for your applications. Plan on spending at least $125,000 to cover freight, setup, fixtures, etc. If you're a new customer your probably looking to fly out a Roehrig engineer for setup and training as well.

    Darren
    Oh yeah thats what I was thinking thanks. Gnarly, but that would be the ultimate geek out tool. Glad I have most of my valving dialed for what I do, the old fashioned way. Lots of test and tune.

    <iframe width="420" height="315" src="http://www.youtube.com/embed/jONt8DdoYPk" frameborder="0" allowfullscreen></iframe>
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    Oh yeah thats what I was thinking thanks. Gnarly, but that would be the ultimate geek out tool. Glad I have most of my valving dialed for what I do, the old fashioned way. Lots of test and tune.
    and the reality is, that's a lowball number. You'd end up spending more.

    In your business though, you most likely relying on FOX or KING for your dampers. FOX has a hydraulic MTS unit and KING uses a Roehrig EMA. I'm assuming that both of those companies would be able to provide force curve specs if your utilizing custom spec shocks?

    Darren

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    Quote Originally Posted by PUSHIND View Post
    and the reality is, that's a lowball number. You'd end up spending more.

    In your business though, you most likely relying on FOX or KING for your dampers. FOX has a hydraulic MTS unit and KING uses a Roehrig EMA. I'm assuming that both of those companies would be able to provide force curve specs if your utilizing custom spec shocks?

    Darren
    Oh yeah I've already ran a few of my tunes on KINGs dyno, just did not know they had the EMA type. That is how I know I'd need the 4k unit, as some of my more aggressive tunes were 3800lbs IIRC(sheets not in front of me).

    I've started dabbling in some more exotic shocks/trucks/vehicles, and it would be so much more time efficient to run the shocks on a machine in house. Sending the shocks off to KING to test, or putting the truck back together, run hard, disassemble, re-do, etc... is so much more time involved.

    Thanks for the input!
    Bend, Oregon

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    If you have the capability to do your own datalogging and analysis, there are very cheap ways to get very high forces at very high velocities

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    Hey Darren,

    What is the application of each type of dyno graph (PVP and CVP)? I mean, what do you look for in each?

    From what I understand, a PVP just records 1 measurement in compression and one in rebound at a selected speed while CVP collects multiple points during compression acceleration and deceleration and rebound acceleration and deceleration.

    I guess CVP is useful for understanding how the fluid behaves and how the shims open and close as well as detect cavitation and hysteresis while PVP is useful for a general representation of the shock behavior. Is this correct?

    Additionally, how come a shock can produce rebound force during compression closed stage? At velocity zero before changing into rebound open, typical dyno graphs show a negative force. How can this be possible?

    Thanks.

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    Ok I just read a document from Roehrig that answers my second question. It states it has a non-zero force because in that instant the shock cannot equalize all internal forces to zero.

  58. #58
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    Quote Originally Posted by PUSHIND View Post
    and the reality is, that's a lowball number. You'd end up spending more.

    In your business though, you most likely relying on FOX or KING for your dampers. FOX has a hydraulic MTS unit and KING uses a Roehrig EMA. I'm assuming that both of those companies would be able to provide force curve specs if your utilizing custom spec shocks?

    Darren
    Lowball yes, don't forget the lexan walls surrounding the unit for bicycle testing on lightweight forks...

    I know that Charlie Curnutt has made bicycle stuff and works with Foes, didn't King make one model of bicycle rear shock for an off brand boutique bike about 15 years ago?

    Ironic how much competition Fox has outside of the bicycle industry. Not that I need them for how I drive, but I am looking at Kings for my Tacoma.

    PK
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    Beanbag, FWIW, getting away from the dyno sheets and speculations stuff, we rode an event this past weekend. Dirt was harder packed than our local sand trails, many more square edges and loose sand on top of shellrock (concreteish).

    We had the Ventana tandem on the trails Friday before the event officially opened. Had the wife take one click out of our DHX 5.0 which took the edge off the square edges, the Fox 40 had me take out 2 clicks of HSC. Still comes down to how it feels as you ride.

    Honestly, if we rode the event trails a lot, I would make a slight shim change to add LSC to the back. The fork would probably dial in. We did ride this weekend on a slightly wallowy setup but it still met the proverbial plush but firm and save the stokers lower back by taking the harshness out via the Propedal setting clicker.

    PK
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    PMK, thanks for bringing this back on topic.

    As mentioned earlier, I changed the compression damping shimstack to reduce the HSC. Right now, the fork is tuned to the point where it is very good about ramming into rocks and roots at around 4-12 mph. Any slower and the front end bounces off, any faster and the impact starts to feel harsh. Also, when the front end is lightly weighted, for example on a slight uphill, it feels kind of skittish over small crumbly rocks, but going over that same section downhill with brakes (front more heavily weighted), the fork actually seems to track that pretty well, with the exception that I can hear little bits of front wheel skidding after it comes off the back side of bumps. What's your take on this?

    Regarding one of your previous comments, how can I tell if my fork is undersprung or not? If I bounce on the fork on purpose I can easily bottom it, and when slowly crawling down a steep hill I probably use up about 65% of my travel in sag alone. But during normal riding, I don't think I use up more than 50%.

  61. #61
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    Quote Originally Posted by tacubaya View Post
    Hey Darren,

    What is the application of each type of dyno graph (PVP and CVP)? I mean, what do you look for in each?

    From what I understand, a PVP just records 1 measurement in compression and one in rebound at a selected speed while CVP collects multiple points during compression acceleration and deceleration and rebound acceleration and deceleration.

    I guess CVP is useful for understanding how the fluid behaves and how the shims open and close as well as detect cavitation and hysteresis while PVP is useful for a general representation of the shock behavior. Is this correct?

    Additionally, how come a shock can produce rebound force during compression closed stage? At velocity zero before changing into rebound open, typical dyno graphs show a negative force. How can this be possible?

    Thanks.
    PVP is only really useful for crank-type dynos where you want to separate position-sensitive and speed-sensitive aspects by taking all velocity measurements at exactly the same point in the travel. It is somewhat usable for generating generic tunes for position-sensitive dampers based purely on leverage ratio but that's about as far as it goes - the CVP plot is generally much more useful. Anyone using PVP for anything other than easy-to-read average values to show the public probably doesn't really know what they're doing.

    I'm not sure what you mean by "rebound force" during the compression closing stage - the force value should definitely not be below zero (positive being defined as in the direction of compression damping force, negative being rebound damping force). Many shocks (esp the RC4) have a substantial enough gas charge force that the gas charge force is much larger than the rebound damping force at low speeds, hence the force at zero speed is actually quite large. Most bike suspension is quite high performance in terms of elasticity and hysteresis; in general the zero velocity points at both TDC and BDC show a net positive force.
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    Quote Originally Posted by Steve VS View Post
    PVP is only really useful for crank-type dynos where you want to separate position-sensitive and speed-sensitive aspects by taking all velocity measurements at exactly the same point in the travel. It is somewhat usable for generating generic tunes for position-sensitive dampers based purely on leverage ratio but that's about as far as it goes - the CVP plot is generally much more useful. Anyone using PVP for anything other than easy-to-read average values to show the public probably doesn't really know what they're doing.

    I'm not sure what you mean by "rebound force" during the compression closing stage - the force value should definitely not be below zero (positive being defined as in the direction of compression damping force, negative being rebound damping force). Many shocks (esp the RC4) have a substantial enough gas charge force that the gas charge force is much larger than the rebound damping force at low speeds, hence the force at zero speed is actually quite large. Most bike suspension is quite high performance in terms of elasticity and hysteresis; in general the zero velocity points at both TDC and BDC show a net positive force.
    Thanks for the response Steve. Didn't think about the position sensitive shocks! I now see where the PVP would come useful.

    Here is a plot where you can see when I mean there is rebound (negative force) being generated on the compression open and rebound closed curves. This phenomenon is explained in Roehrig "Why is there a force value at zero velocity?" tech document.

    Last edited by tacubaya; 11-12-2012 at 09:51 PM.

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    What you're seeing there is actually the CO/RC curve (have a similar effect on my own measurements with certain settings). I believe on the CCDB, that effect is caused by the rebound poppet valve which increases the effective elasticity of the system as its closing characteristic is distinctly different to its opening characteristic - meaning that even after the zero velocity point, the rebound poppet is still closing and displacing oil in the direction opposing the rebound stroke (acting to compress the shock). This effect occurs most visibly when the LSR is fully closed, which prevents the oil displaced by the HS poppet from recirculating through the LS circuit.
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  64. #64
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    Quote Originally Posted by tacubaya View Post
    Ok I just read a document from Roehrig that answers my second question. It states it has a non-zero force because in that instant the shock cannot equalize all internal forces to zero.
    Steve posted sort of the exact same within more specifics given. Suspension is always a best compromise, and where the freebleeds are positioned, along with the specific valving can create almost an inertia type occurrence.

    Consider also, that in true HSC events, as was shown in the video link I posted, the cavitated fluid is also reabsorbing. The variables can have this take an instant or even longer which may contribute to a portion of the "inertia".

    I must say that Steves perspective on the data displayed is great. It validates how the dyno plots can seem impressive. But the real data is for those that understand what they see. I will get killed for saying it, regardless of what the dyno states, you still need to ride it.

    A bicycle two post dyno with high ipds values would be the ultimate...if someone built it. Truly showing not just how the damper performs but showing how the damper performs while coupled to the effects of leverage ratios, and pivot paths.

    PK
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    Quote Originally Posted by beanbag View Post
    PMK, thanks for bringing this back on topic.

    As mentioned earlier, I changed the compression damping shimstack to reduce the HSC. Right now, the fork is tuned to the point where it is very good about ramming into rocks and roots at around 4-12 mph. Any slower and the front end bounces off, any faster and the impact starts to feel harsh. Also, when the front end is lightly weighted, for example on a slight uphill, it feels kind of skittish over small crumbly rocks, but going over that same section downhill with brakes (front more heavily weighted), the fork actually seems to track that pretty well, with the exception that I can hear little bits of front wheel skidding after it comes off the back side of bumps. What's your take on this?

    Regarding one of your previous comments, how can I tell if my fork is undersprung or not? If I bounce on the fork on purpose I can easily bottom it, and when slowly crawling down a steep hill I probably use up about 65% of my travel in sag alone. But during normal riding, I don't think I use up more than 50%.
    My take, and realize I have not seen the terrain nor the bike ridden by you in the terrain. Sounds as if the HSC has been set to handle your average window of speed. This is good but may get better. The harshness at faster speeds indicates that, and this can be tough with few shims in a bicycle suspension, the cartridge is still holding pressure. Consider that all shims combined rather than specific single shims make the stack change.

    Your comment about skittery on rocks, sometimes this just happens and is something to just ride, however, this may indicate to much mid speed control.

    Again, the total combination of shims or fluid paths determine peak values. Some areas to look closely and test could be running a smaller clamp diameter, this will widen your HSC window and lessen the MS. In not altering clamp diameter, you might find that a change in the stacking aspect ratio for the later portion of the stack could help. Explained, rather than jump shims on 2mm diameter changes, jump 3mm per step while retaining the same thickness.

    The small net change to LSC can often be adjusted out via the freebleed setting.

    As for spring rates. I don't know your exact setup or settings. There is more to the spring than just rate and sag values. Sag values can vary from rider to rider, but often fall within a 15 to 30 percent range based on total travel. Many bicycle forks have little ramp up of the air spring, so much of the feel is linear. In my opinion, a good design needs the air spring function to add progression, in many cases to match the rear. It is possible you are on the firmer side of spring selection and could benefit from a lighter spring IF you can add progression. This may help with the small rocks and getting through that, but consider you still need the same net spring force during mid stroke.

    As cobby as they were, old style forks with elastomers on a skewer had the ability to make a totally linear style fork progressive by allowing the owner to build a spring specific to their style plus control bottoming.

    If the fork uses any style of hydraulic bottoming circuits, these too may be far too effective and require changes to realize full travel.

    My apologies for not having an exact answer. Maybe it has given some insight of other options.

    After rereading your post, if you have concern about the skidding on situations that unload the suspension such as the back side of bumps. That to me sounds very good. Max braking for a given weight bias and suspension setting. Consider that the skid is followed by a next bump which will fully optimize the grip / brakes. To change this is a change in rider technique. What you describe freaks out those not capable of riding with confidence of using a front brake 100%.

    Again, it is nothing more than a best compromise.

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    Quote Originally Posted by Steve VS View Post
    What you're seeing there is actually the CO/RC curve (have a similar effect on my own measurements with certain settings). I believe on the CCDB, that effect is caused by the rebound poppet valve which increases the effective elasticity of the system as its closing characteristic is distinctly different to its opening characteristic - meaning that even after the zero velocity point, the rebound poppet is still closing and displacing oil in the direction opposing the rebound stroke (acting to compress the shock). This effect occurs most visibly when the LSR is fully closed, which prevents the oil displaced by the HS poppet from recirculating through the LS circuit.
    Yup, it is RC/CO, my bad!

    Thanks for the explanation.

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    Quote Originally Posted by PMK View Post
    Steve posted sort of the exact same within more specifics given. Suspension is always a best compromise, and where the freebleeds are positioned, along with the specific valving can create almost an inertia type occurrence.

    Consider also, that in true HSC events, as was shown in the video link I posted, the cavitated fluid is also reabsorbing. The variables can have this take an instant or even longer which may contribute to a portion of the "inertia".

    I must say that Steves perspective on the data displayed is great. It validates how the dyno plots can seem impressive. But the real data is for those that understand what they see. I will get killed for saying it, regardless of what the dyno states, you still need to ride it.

    A bicycle two post dyno with high ipds values would be the ultimate...if someone built it. Truly showing not just how the damper performs but showing how the damper performs while coupled to the effects of leverage ratios, and pivot paths.

    PK
    Yeah, I thought it was RO/CC stage so I couldn't figure out what was going on, but once Steve made me realize it is RC/CO stage, everything makes sense now.

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    Quote Originally Posted by PMK View Post
    A bicycle two post dyno with high ipds values would be the ultimate...if someone built it. Truly showing not just how the damper performs but showing how the damper performs while coupled to the effects of leverage ratios, and pivot paths.

    PK
    I built a single post shaker for a bike as part of my undergrad thesis about five years ago. It was pretty crude (budget was about $100 other than the inverter and the sensors which I borrowed) and could only do sine waves, all you could do was vary amplitude/frequency. There was a linear pot between the base plate and the moving floor, and another one mounted between the shock eyes. It was basically built to investigate the interaction between mechanical and biomechanical motion at different frequencies - the aim was to generate a mathematical model of a rider as a part of the suspension, but that was only partly successful as the rider is an active element rather than a passive element at certain frequencies. Was kind of sketchy at high frequencies because a rider obviously has to be on the bike while it's getting kicked up and down!

    Video of the rig here: Test Rig First Trial - YouTube
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    This is where it needs to be.

    ROEHRIG ENGINEERING INC

    However, I do believe that with enough computing power, knowledge and skill, an EMA can take suspension plots from data logging, convert it into programs that the dyno can play, not only in regards to terrain but also suspension paths created via linkage or with rear suspension moving in arcs. Regardless though, a post setup will find mechanical concerns but a rolling setup with ema would be best.

    Somehow this is going to get expensive for a silly little bicycle.

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    Quote Originally Posted by PMK View Post
    This is where it needs to be.

    ROEHRIG ENGINEERING INC

    However, I do believe that with enough computing power, knowledge and skill, an EMA can take suspension plots from data logging, convert it into programs that the dyno can play, not only in regards to terrain but also suspension paths created via linkage or with rear suspension moving in arcs. Regardless though, a post setup will find mechanical concerns but a rolling setup with ema would be best.

    Somehow this is going to get expensive for a silly little bicycle.

    PK
    I have actually put a great deal of thought into these, and concluded that there is no practical way to simulate all the required motions, forces and accelerations without the rider/bike actually moving around a very long way unless you had a rolling road that can vary both its gradient and its profile - ie multimillion dollar custom setups. Easier than that would just be datalogging on the trail with simultaneous logging of suspension displacement, strain gauges in appropriate locations (to derive force against velocity) as well as a couple of high-G accelerometers to look at pitch and bounce stability. Again, easily talking $25k+ of electronics here.
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    But for normal people, we should adjust our suspension properly and if we can't adjust it to our satisfaction, then we consult profession tuners who can make the necessary modifications and/or suggest a different shock/fork which can be modified and tuned to suit.

    I think this thread has been very, very informative about what is really going on with the suspension, but for Joe Mountainbiker, it's unnecessarily deep. There is an unfortunate number of people who don't know what the knobs do (easily solved) or can't interpret what they are feeling on the trail and make the right adjustment (not as easy).

  72. #72
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    Quote Originally Posted by Steve VS View Post
    I have actually put a great deal of thought into these, and concluded that there is no practical way to simulate all the required motions, forces and accelerations without the rider/bike actually moving around a very long way unless you had a rolling road that can vary both its gradient and its profile - ie multimillion dollar custom setups. Easier than that would just be datalogging on the trail with simultaneous logging of suspension displacement, strain gauges in appropriate locations (to derive force against velocity) as well as a couple of high-G accelerometers to look at pitch and bounce stability. Again, easily talking $25k+ of electronics here.
    If there is a will there is a way...Honestly though, it would settle the debates about what designs are good or bad to compress a shock and follow the ground.

    A semi rolling road is easy, round drum with changeable "bumps". Bump height offers displacement while drum RPM offers IPS. "Bump" profile can show results of fore aft binding.

    Really, I don't miss being a suspension guy anymore. Far easier and less headaches to enjoy someone else becoming famous.

    PK
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  73. #73
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    Quote Originally Posted by ColinL View Post
    But for normal people, we should adjust our suspension properly and if we can't adjust it to our satisfaction, then we consult profession tuners who can make the necessary modifications and/or suggest a different shock/fork which can be modified and tuned to suit.

    I think this thread has been very, very informative about what is really going on with the suspension, but for Joe Mountainbiker, it's unnecessarily deep. There is an unfortunate number of people who don't know what the knobs do (easily solved) or can't interpret what they are feeling on the trail and make the right adjustment (not as easy).
    Not to worry, the majority of moto guys have no clue either. The topic of HSC gets very in depth and is worse for Joe Mountainbiker on account that most suspension designs are not capable of externally adjusting HSC.

    When you learn about HSC, which is this topic, you quickly realize that there is more to it than just square edge bumps. It also serves as a ride height tool and can minimize wallowing effect while allowing average freebleed settings.

    When HSC is wrong, it's as if nothing can make the fork good.

    Oddly, none of us can decide on where exactly HSC occurs in the Inches Per Second. I am often condemned for IPS to high, while others favor a lower number.

    Therefore HSC can be a moving target, especially when the rider can not recognize it or know how to work with it.

    PK
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  74. #74
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    Quote Originally Posted by Steve VS View Post
    I built a single post shaker for a bike as part of my undergrad thesis about five years ago. It was pretty crude (budget was about $100 other than the inverter and the sensors which I borrowed) and could only do sine waves, all you could do was vary amplitude/frequency. There was a linear pot between the base plate and the moving floor, and another one mounted between the shock eyes. It was basically built to investigate the interaction between mechanical and biomechanical motion at different frequencies - the aim was to generate a mathematical model of a rider as a part of the suspension, but that was only partly successful as the rider is an active element rather than a passive element at certain frequencies. Was kind of sketchy at high frequencies because a rider obviously has to be on the bike while it's getting kicked up and down!

    Video of the rig here: Test Rig First Trial - YouTube
    Ah yeah I remember that. It took me a while to read your thesis. I remember that in one part you talk about how the position sensitive shock (DHX) generated hysteresis in the CVP plot.

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    PMK - thank you for the comments.

    I finally got around to doing the critical damping calculation. The formula being sqrt(spring constant * mass). The rationale for this formula is that once the front wheel hits a bump and gets accelerated, it shouldn't keep flying towards the bike. This is just a really rough guideline, though. For example, the tire being connected to the ground adds an additional spring.

    I figured a spring constant of about 200 lbs / 4 inches, and a front wheel + fork lowers mass of 2.4 kg. Using these numbers, I came up with 146 kg/s. Here it is plotted on the Manitou ABS+ tuning manual:



    The blue line was what I ended up settling on when riding on the trail (before I even did this calculation). It turns out that the damping is set about right for 8-24 ips. According to this metric, there is still too much high speed damping, like you suggested.

    This is not the first time that this has happened, where I measure the current settings of the shock and find out that it is pretty close to some mathematically recommended value.

    It turns out that Manitou has another recommended shim stack which more closely matches the guideline:



    The LSC platform slope should probably be some fraction of the critical damping for spring constant and rider weight.

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    Quote Originally Posted by beanbag View Post
    PMK - thank you for the comments.

    I finally got around to doing the critical damping calculation. The formula being sqrt(spring constant * mass). The rationale for this formula is that once the front wheel hits a bump and gets accelerated, it shouldn't keep flying towards the bike. This is just a really rough guideline, though. For example, the tire being connected to the ground adds an additional spring.

    I figured a spring constant of about 200 lbs / 4 inches, and a front wheel + fork lowers mass of 2.4 kg. Using these numbers, I came up with 146 kg/s. Here it is plotted on the Manitou ABS+ tuning manual:



    The blue line was what I ended up settling on when riding on the trail (before I even did this calculation). It turns out that the damping is set about right for 8-24 ips. According to this metric, there is still too much high speed damping, like you suggested.

    This is not the first time that this has happened, where I measure the current settings of the shock and find out that it is pretty close to some mathematically recommended value.

    It turns out that Manitou has another recommended shim stack which more closely matches the guideline:



    The LSC platform slope should probably be some fraction of the critical damping for spring constant and rider weight.
    What type of vibration system are you modelling to obtain the cc= sqrt(m*k)?

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    Quote Originally Posted by Steve VS View Post
    What you're seeing there is actually the CO/RC curve (have a similar effect on my own measurements with certain settings). I believe on the CCDB, that effect is caused by the rebound poppet valve which increases the effective elasticity of the system as its closing characteristic is distinctly different to its opening characteristic - meaning that even after the zero velocity point, the rebound poppet is still closing and displacing oil in the direction opposing the rebound stroke (acting to compress the shock). This effect occurs most visibly when the LSR is fully closed, which prevents the oil displaced by the HS poppet from recirculating through the LS circuit.
    I think what you will also find is that a poppet-type valve behaves differently under an accelerating stroke vs a decelerating stroke, even when it is not near the turn-around point. Here is a dyno plot of a twin-tube shock which has a poppet valve on the compression side (negative force) and shims + bleed on the rebound side. I excised the data near the turn-around points, so everything is mid-stroke. The input is more or less an arbitrary waveform (LOL) of increasing frequency. This way, I have a sampling of points with all kinds of position, velocity, and acceleration (LOL). I might have also screwed up and said accelerating instead of decelerating.



    Look how clean the rebound side is vs the compression.
    In any case, on a crank-type dyno, it puts the points of maximal acceleration right near the turn-around point, so these effects are combined.

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    Quote Originally Posted by tacubaya View Post
    What type of vibration system are you modelling to obtain the cc= sqrt(m*k)?
    ehhh, what's a factor of 2 btw friends.

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    Quote Originally Posted by beanbag View Post
    PMK - thank you for the comments.

    I finally got around to doing the critical damping calculation. The formula being sqrt(spring constant * mass). The rationale for this formula is that once the front wheel hits a bump and gets accelerated, it shouldn't keep flying towards the bike. This is just a really rough guideline, though. For example, the tire being connected to the ground adds an additional spring.

    I figured a spring constant of about 200 lbs / 4 inches, and a front wheel + fork lowers mass of 2.4 kg. Using these numbers, I came up with 146 kg/s. Here it is plotted on the Manitou ABS+ tuning manual:



    The blue line was what I ended up settling on when riding on the trail (before I even did this calculation). It turns out that the damping is set about right for 8-24 ips. According to this metric, there is still too much high speed damping, like you suggested.

    This is not the first time that this has happened, where I measure the current settings of the shock and find out that it is pretty close to some mathematically recommended value.

    It turns out that Manitou has another recommended shim stack which more closely matches the guideline:



    The LSC platform slope should probably be some fraction of the critical damping for spring constant and rider weight.
    A couple of things to note:
    1. You are saying 146kg/s damping coefficient (usually given in N.s/m so not really sure how you arrived at this number) then at 1m/s you appear to be reading off 146N, not 146kg.
    2. The actual formula for a critical damping rate is c = 2*sqrt(k*m), which using the values you have given, actually spits out about 290N.s/m.
    3. Damping ratio calculations are typically applied to sprung masses not unsprung masses, and in the case of a bicycle, they are not mathematically indicative of anything that is actually useful.
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    Quote Originally Posted by beanbag View Post
    I think what you will also find is that a poppet-type valve behaves differently under an accelerating stroke vs a decelerating stroke, even when it is not near the turn-around point. Here is a dyno plot of a twin-tube shock which has a poppet valve on the compression side (negative force) and shims + bleed on the rebound side. I excised the data near the turn-around points, so everything is mid-stroke. The input is more or less an arbitrary waveform (LOL) of increasing frequency. This way, I have a sampling of points with all kinds of position, velocity, and acceleration (LOL). I might have also screwed up and said accelerating instead of decelerating.

    Look how clean the rebound side is vs the compression.
    In any case, on a crank-type dyno, it puts the points of maximal acceleration right near the turn-around point, so these effects are combined.
    I did specifically mention that the opening and closing characteristics of a poppet valve are distinctly different, and that this was the cause. As a rule of thumb, the stiffer the valve's static displacement characteristic and the lower the initial preload, the less hysteresis between opening and closing characteristics.
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  81. #81
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    Beanbag, also consider that it is always easier to ride a firmer setup than softer setup. Work to maintain firm in the mid stroke, and slightly less HSC if possible based on your available shims.

    This may even require a preload style shim for mid speed stuff and a crossover for better LSC, ultimately topped off with a small clamp.

    Another option may be with non-floating shims to punch a heavier face shim with small relief holes towards the shims outer edge. This can, if done properly, trick the shims into seeing two different pressure values to unseat the stack. Basically it is the concept of getting two port sizes from one valve body. The ported shim will apply pressure differently onto the next shim and can increase LSC and MSC while retaining lower HSC values. Bit of work and requires proper shim indexing on each installation.

    Try what your graphs plot settings suggest, however I suspect you are experiencing more than 24 IPS and exceeding the values you are working with. Try plots out towards at least 40, see if those stacks can be built. I would not expect they can without spiking.

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    Quote Originally Posted by Steve VS View Post
    A couple of things to note:
    1. You are saying 146kg/s damping coefficient (usually given in N.s/m so not really sure how you arrived at this number) then at 1m/s you appear to be reading off 146N, not 146kg.
    2. The actual formula for a critical damping rate is c = 2*sqrt(k*m), which using the values you have given, actually spits out about 290N.s/m.
    3. Damping ratio calculations are typically applied to sprung masses not unsprung masses, and in the case of a bicycle, they are not mathematically indicative of anything that is actually useful.
    Steve, work out the units for N*s/m.
    I think I plotted it correctly, except the factor of 2. I can always reverse justify and claim that .5 critical damping is what you are aiming for LOL. For example, a typical "fastest settling time" is for slightly under-damped, like .6-.7. This constant is typically used for LSR on car stuff.

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    Quote Originally Posted by beanbag View Post
    Steve, work out the units for N*s/m.
    I think I plotted it correctly, except the factor of 2. I can always reverse justify and claim that .5 critical damping is what you are aiming for LOL. For example, a typical "fastest settling time" is for slightly under-damped, like .6-.7. This constant is typically used for LSR on car stuff.
    You are playing with vibration mechanics without understanding it.

    As Steve states, the mass is sprung mass, not unsprung. Generating a vibration model of a rider on a bike is pretty difficult, if you don't believe me you have to read Steve's undergrad thesis.

    Even if you succeed in generating a SDOF model of the front fork with linear damping and half the rider mass (assuming 50-50 weight distribution) plus mass of some bike components , the closest model is a forced non-periodic vibration. Additionally due to transmissibility, in some frequencies you definitely don't want critical damping.

  84. #84
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    Quote Originally Posted by tacubaya View Post

    As Steve states, the mass is sprung mass, not unsprung.
    Which is why I said earlier that :

    "The LSC platform slope should probably be some fraction of the critical damping for spring constant and rider weight."

    I figure that low speed damping has to do with sprung weight and high speed to do with unsprung. You disagree?

    Generating a vibration model of a rider on a bike is pretty difficult, if you don't believe me you have to read Steve's undergrad thesis.
    link to thesis then

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    Quote Originally Posted by beanbag View Post
    Which is why I said earlier that :

    "The LSC platform slope should probably be some fraction of the critical damping for spring constant and rider weight."

    I figure that low speed damping has to do with sprung weight and high speed to do with unsprung. You disagree?



    link to thesis then
    Yes I disagree. What you are calculating is just math gibberish.

    About the thesis, you are asking the wrong guy... try with Steve.

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    Quote Originally Posted by tacubaya View Post
    Yes I disagree. What you are calculating is just math gibberish.
    So the next question would be "Do you think there are any mathematical justifications for setting HSC, including rolling in whatever factors you want?"

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    Quote Originally Posted by beanbag View Post
    So the next question would be "Do you think there are any mathematical justifications for setting HSC, including rolling in whatever factors you want?"
    Interesting counter post.

    My opinion would lean towards heading back towards a HSC dyno run where rider mass, sprung mass and even unsprung mass is not a true factor. Merely the ability to see the dyno plot and compare it to reasonably attained HSC values.

    Know the LSC values and plot the riders preference to aim for connecting the end points.

    The bicycle is too light, and rider mass inconsistent in both static and dynamic placements, add to that the riders own ability to lock their elbows or not lock elbows (knees also) and the type of impact is tossed out the window.

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    Quote Originally Posted by PMK View Post
    The bicycle is too light, and rider mass inconsistent in both static and dynamic placements, add to that the riders own ability to lock their elbows or not lock elbows (knees also) and the type of impact is tossed out the window.

    PK
    Add to that riding style, ability, terrain, and intent on that bike... Too many variables with bicycles. I can make my bike bottom out on flat ground not moving at all. Try that with a Moto.

    Side note.. I crack up with the factual statements in suspension tuning. The best example that comes to mind is "landing from a jump is a LSC event". Give me a break. Did you land on the backside of a transition, or into one? Did the tires come 8" off the ground, or 8'?
    Bend, Oregon

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    Quote Originally Posted by beanbag View Post
    So the next question would be "Do you think there are any mathematical justifications for setting HSC, including rolling in whatever factors you want?"
    Due to the nature of the mass (dynamic, active and with instant distribution changes) and the range of velocities, styles, terrains and whatnot I believe a mathematical model that serves as to setup HSC is unrealistic and far too complex.

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    Quote Originally Posted by thuren View Post
    Add to that riding style, ability, terrain, and intent on that bike... Too many variables with bicycles.
    How is Push able to rake in money hand-over-fist by giving people the perfect valving, and all they ask for is rider weight, riding style (plush, aggressive, race, etc), and whether or not you live in Florida? That's like 3 variables (the rest, like bike and shock type are known) and they can come up with a recipe. They know how much high speed damping to give somebody, although obviously they won't say because it is their secret sauce. They don't need to fly an engineer out to every customer with a box of shims and ride along with him on the trail, turning his knobs.

  91. #91
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    Quote Originally Posted by tacubaya View Post
    Due to the nature of the mass (dynamic, active and with instant distribution changes) and the range of velocities, styles, terrains and whatnot I believe a mathematical model that serves as to setup HSC is unrealistic and far too complex.
    I think you would be missing the point by trying to model a bobble-head rider pitching back and forth over "forced non-periodic vibrations" LOL. All I am asking for is a recipe or formula or guideline that tells you how much high speed damping to use.

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    Quote Originally Posted by beanbag View Post
    How is Push able to rake in money hand-over-fist by giving people the perfect valving, and all they ask for is rider weight, riding style (plush, aggressive, race, etc), and whether or not you live in Florida? That's like 3 variables (the rest, like bike and shock type are known) and they can come up with a recipe. They know how much high speed damping to give somebody, although obviously they won't say because it is their secret sauce. They don't need to fly an engineer out to every customer with a box of shims and ride along with him on the trail, turning his knobs.
    There is no perfect valving, suspension is all about compromises.

  93. #93
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    Quote Originally Posted by beanbag View Post
    I think you would be missing the point by trying to model a bobble-head rider pitching back and forth over "forced non-periodic vibrations" LOL. All I am asking for is a recipe or formula or guideline that tells you how much high speed damping to use.
    Ok here it goes:

    2 parts of knowledge
    1 part dyno
    1 part data acquisition
    add riding time until consistency is good

    Serve cold.

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    Quote Originally Posted by beanbag View Post
    How is Push able to rake in money hand-over-fist by giving people the perfect valving, and all they ask for is rider weight, riding style (plush, aggressive, race, etc), and whether or not you live in Florida?
    Empirical testing and data acquisition... They get the damping ratios and such off from what the dyno tells them are good ranges when compared with the information provided by riders (during testing phase) and on-board data acquisition.

    They take a plot of a good run, calculate values "in the ballpark", design a damper that may present those characteristics sought and they go back to the trail to test for another iteration of the process.

    Agreed that a really approximate model is too complex to be worth the money (at least for mountain bikes applications) and you're better off with experience and data acquisition.

    No doubt that somewhere somehow they have math models for suspension design (MX? F1? Military applications?) but you have to have the market to trigger the development. The average cyclist can hardly set up sag correctly (no offense) and most select equipment based on weight, colour and lockouts, they don't know what suspension works best for them.

    As for guidelines or formulas, I don't think any suspension tuner will share them. At least not in the bicycle field and no other application comes close to bicycles for the same reasons others have mentioned, so transposing them is kind of difficult. It's part of their know how.

    There are so many variables that your best bet is data logging.
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    Quote Originally Posted by beanbag View Post
    How is Push able to rake in money hand-over-fist by giving people the perfect valving...
    They might be raking in the money but they can't give people "perfect valving". All they can attempt to do is provide "better" or improved.

    Improved offerings may be easy where there is a known limitation in a suspension component like ports on a compression piston that are too small to prevent spiking or a port orifice only rebound damper that can be replaced with a shimmed damper.

    Beyond that the gains are more incremental and harder to quantify when put into the hands of the rider.

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    I used "perfect" hyperbolically...

    but those are good responses anyway

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    WTH does 'raking in money' have to do with anything? every business exists to make a profit. any business that doesn't make a profit ceases to exist. (except the government... )

    1. would the MTB community be better off if PUSH didn't exist?

    2. if you think PUSH's prices are too high, or their products & services unworthy of the cost, doesn't that simply serve to create competition?

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    How is Push able to rake in money hand-over-fist by giving people the perfect valving, and all they ask for is rider weight, riding style (plush, aggressive, race, etc), and whether or not you live in Florida? That's like 3 variables (the rest, like bike and shock type are known) and they can come up with a recipe. They know how much high speed damping to give somebody, although obviously they won't say because it is their secret sauce. They don't need to fly an engineer out to every customer with a box of shims and ride along with him on the trail, turning his knobs.
    First off, I don't think anyone in the bicycle industry is making money "hand-over-fist". It's a small industry of mostly passionate people. Prior to PUSH I had a successful career in Motorsports which would have net me more money over the years than PUSH has. The amount of personal sacrifice myself and my family have had to make to create this brand and company at times has seemed insurmountable. But, at the end of the day I love what I do, we've created jobs in our community, and have provided income to vendors both in our community and around our nation. It's a big picture thing. And, again I love what I do.

    As for what we do...it's not perfect. Suspension is a compromise. Anyone who tells you different lacks experience. Several factors play into our business.

    1. Experience. I'm an avid enthusiast and got my start at Marzocchi in 1993. So, for nearly two decades I've been riding and developing suspension components for MTB's and Motorcycles. We also have a database of feedback from thousands of customers from our nearly 10 years in business. Some positive, some negative....all of it valuable.

    2. Research tools. Obviously it's all ready been stated in this post, but we employ lots of riding with a lot of state-of-the-art tools, to continually test and develop. Most importantly, we all ride the stuff.

    3. Details. Most customers don't just hand over their rider weight, style, and bike. Most people either fill the notes field of their web order with information, or provide it over the phone when placing an order for service. This one-on-one model allows us to better understand the customers expectations as well as allow us to understand what they do, and don't like about what they're sending in.

    4. After Service. We provide industry leading support via phone or email after you've received your suspension back from us. If you have questions about what to adjust, or how something effects your setup, the person who built your suspension is just a phone call or email away.

    5. If all else fails. Fortunately we don't have to use it much, but we offer a revalve guarantee. If within the first few weeks of riding your stuff and working with the techs you find that it's not what you were looking for, simply pay the shipping and we'll reconfigure it for you at no charge. We've provided this since day one.

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    Quote Originally Posted by beanbag View Post
    All I am asking for is a recipe or formula or guideline that tells you how much high speed damping to use.
    Need something similar to how they map Google Earth, except w/ a fork chunk-o-meter ...

    People of different weight, say in 25lb increments, could ride single file up/down trails (with dh/fr, am/xc chunk-o-meters) and map a MTBR Earth : D

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    Quote Originally Posted by PUSHIND View Post
    First off, I don't think anyone in the bicycle industry is making money "hand-over-fist". It's a small industry of mostly passionate people. Prior to PUSH I had a successful career in Motorsports which would have net me more money over the years than PUSH has. The amount of personal sacrifice myself and my family have had to make to create this brand and company at times has seemed insurmountable. But, at the end of the day I love what I do, we've created jobs in our community, and have provided income to vendors both in our community and around our nation. It's a big picture thing. And, again I love what I do.

    As for what we do...it's not perfect. Suspension is a compromise. Anyone who tells you different lacks experience. Several factors play into our business.

    1. Experience. I'm an avid enthusiast and got my start at Marzocchi in 1993. So, for nearly two decades I've been riding and developing suspension components for MTB's and Motorcycles. We also have a database of feedback from thousands of customers from our nearly 10 years in business. Some positive, some negative....all of it valuable.

    2. Research tools. Obviously it's all ready been stated in this post, but we employ lots of riding with a lot of state-of-the-art tools, to continually test and develop. Most importantly, we all ride the stuff.

    3. Details. Most customers don't just hand over their rider weight, style, and bike. Most people either fill the notes field of their web order with information, or provide it over the phone when placing an order for service. This one-on-one model allows us to better understand the customers expectations as well as allow us to understand what they do, and don't like about what they're sending in.

    4. After Service. We provide industry leading support via phone or email after you've received your suspension back from us. If you have questions about what to adjust, or how something effects your setup, the person who built your suspension is just a phone call or email away.

    5. If all else fails. Fortunately we don't have to use it much, but we offer a revalve guarantee. If within the first few weeks of riding your stuff and working with the techs you find that it's not what you were looking for, simply pay the shipping and we'll reconfigure it for you at no charge. We've provided this since day one.

    Darren
    0.5. You sort something most people would never figure on their own.

    I see some in this thread that sure would, but the wast majority, would simply never put in that much effort.


    Magura

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