Page 1 of 5 1 2 3 4 5 LastLast
Results 1 to 25 of 105
  1. #1
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,698

    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
    What?
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,211
    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
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    1,277
    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
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    1,277
    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
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,698
    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?

  6. #6
    What?
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,211
    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.

  7. #7
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    1,277
    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
    Serenity now!
    Reputation: PixieChik's Avatar
    Join Date
    Jul 2010
    Posts
    239
    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)

  9. #9
    mtbr member
    Reputation:
    Join Date
    Nov 2009
    Posts
    703
    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.

  10. #10
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,698
    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
    What?
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,211
    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
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,698
    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.

  13. #13
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    1,277
    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
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    1,277
    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.

  15. #15
    mtbr member
    Reputation: PUSHIND's Avatar
    Join Date
    Jan 2004
    Posts
    1,635
    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
    mtbr member
    Reputation: ColinL's Avatar
    Join Date
    Feb 2012
    Posts
    1,277
    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
    What?
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,211
    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
    What?
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,211
    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
    PMK
    PMK is offline
    mtbr member
    Reputation: PMK's Avatar
    Join Date
    Oct 2004
    Posts
    2,246
    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  

    Reps! We don't need no stickin' reps!

  20. #20
    mtbr member
    Reputation: PUSHIND's Avatar
    Join Date
    Jan 2004
    Posts
    1,635
    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
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,698
    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
    Save Jesus
    Reputation: beanbag's Avatar
    Join Date
    Nov 2005
    Posts
    2,698
    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.

  23. #23
    mtbr member
    Reputation: PUSHIND's Avatar
    Join Date
    Jan 2004
    Posts
    1,635
    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

  24. #24
    What?
    Reputation: mullen119's Avatar
    Join Date
    Aug 2009
    Posts
    3,211
    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

  25. #25
    mtbr member
    Reputation:
    Join Date
    Oct 2012
    Posts
    113
    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....


Page 1 of 5 1 2 3 4 5 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •