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  1. #1
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    Does anybody have Suspension Velocity Data?

    Back when I was doing race car suspension, I had the ability to data log suspension position over time, which a quick bit of calculus (happily, done by a math channel in the logger software) could turn into suspension velocity.

    With that data, you could see what kind of shaft speeds the shocks were seeing, and tune accordingly. For example, it became clear that speeds under 3 in/sec were suspension moving in response to dynamics, and over 3 in/sec was bumps in the pavement.

    I'd love to see some MTB suspension data. Does anybody have any?

    DG

  2. #2
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    Maybe I'll get around to it when I feel like making some mounting brackets and buying a netbook.

  3. #3
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    I'd love to work with this kind of stuff too... creating some nice charts, and using shimrestackor.com to create the perfect damper for my riding

  4. #4
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    We use data loggers here at PUSH. Here's some data from a local trail.

    Darren
    Attached Thumbnails Attached Thumbnails Does anybody have Suspension Velocity Data?-travel-bottoming.jpg  

    Does anybody have Suspension Velocity Data?-velocity.jpg  


  5. #5
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    I'm also interested about this information for shock tuning purposes. Excellent info Darren, thank you for sharing that! Very interesting data and charts.

  6. #6
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    Quote Originally Posted by two-one View Post
    I'd love to work with this kind of stuff too... creating some nice charts, and using shimrestackor.com to create the perfect damper for my riding
    Shim Restackor has limited usefulness in a market full of dampers with position sensitive features, secondary compression adjusters etc.

  7. #7
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    80 in/sec peaks. Wow.

    That's a lot of range to cover.

    DG

  8. #8
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    Quote Originally Posted by RecceDG View Post
    80 in/sec peaks. Wow.

    That's a lot of range to cover.

    DG
    That's what speed sensitive damping is for

    Btw, those kind of speeds are not rare.

  9. #9
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    That's what speed sensitive damping is for
    All dampers are, by definition, speed-sensitive.

    It is position sensitive dampers that are rare (like the Bilstein off-road race truck dampers)

    DG

  10. #10
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    Quote Originally Posted by RecceDG View Post
    All dampers are, by definition, speed-sensitive.

    It is position sensitive dampers that are rare (like the Bilstein off-road race truck dampers)

    DG
    Yeah, rare, only half the shocks out there have it (Boostvalve).

    I thought it was accepted among the suspension tech community to call variable port "size" (using shims, poppets etc.) speed sensitive in the sense that as speed, and thereby flow increases, the flow area increases but whatever, if you want to be all smarty pants then let me rephrase:

    That is what shimmed dampers are for.

  11. #11
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    It is accepted in the suspension tech community to call dampers "speed sensitive" only so far as that is how they work. A damper produces no force unless it is moving; unlike a spring that produces force whenever compressed. A damper has no choice but to be "speed sensitive" so calling a damper "speed sensitive" is meaningless.

    Flow area must increase with increased damper speed, because if you don't, the force curve is sharply progressive and at some point the force produced is so high that the damper effectively locks solid.

    A basic, no-frills damper scales flow area in proportion to shaft speed such that the force/speed ratio is linear. More sophisticated dampers provide one or more regions of digressive forces (a "knee" in the force curve) to better react to faster speeds. We typically digressed from 0.65 DR to 0.3 DR at about 3 in/sec in the race cars, and anything over 30 in/sec was very rare.

    A shimstack damper is one way to get a linear force curve, yes. Any mechanism that produces larger flow areas in proportion to increased shaft speed can, in theory, do the same job.

    DG

  12. #12
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    Quote Originally Posted by RecceDG View Post
    It is accepted in the suspension tech community to call dampers "speed sensitive" only so far as that is how they work. A damper produces no force unless it is moving; unlike a spring that produces force whenever compressed. A damper has no choice but to be "speed sensitive" so calling a damper "speed sensitive" is meaningless.

    Flow area must increase with increased damper speed, because if you don't, the force curve is sharply progressive and at some point the force produced is so high that the damper effectively locks solid.

    A basic, no-frills damper scales flow area in proportion to shaft speed such that the force/speed ratio is linear. More sophisticated dampers provide one or more regions of digressive forces (a "knee" in the force curve) to better react to faster speeds. We typically digressed from 0.65 DR to 0.3 DR at about 3 in/sec in the race cars, and anything over 30 in/sec was very rare.

    A shimstack damper is one way to get a linear force curve, yes. Any mechanism that produces larger flow areas in proportion to increased shaft speed can, in theory, do the same job.

    DG
    No sh1t...

  13. #13
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    The maximal shock/fork velocity data is not that interesting because all you need to do is make sure you are not cavitating or hydrolocking on the compression stroke. You can determine this even if your dynometer has a much lower maximal speed for testing. The rebound stroke also has an upper limit because of the maximum extension force of the fork (maybe about 1.5-2x body weight).

    Beyond that, tuning seems to be mostly about knowing what LCS, LSR, HSC, HSR, etc feel like on the trail. In the little time I spent on it, I haven't been able to get much out of analyzing shock velocity data like histograms, transient response, fourier transform, etc. This is why I am not a professional shock tuner, LOL.

  14. #14
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    Quote Originally Posted by RecceDG View Post
    Flow area must increase with increased damper speed, because if you don't, the force curve is sharply progressive and at some point the force produced is so high that the damper effectively locks solid.
    The bike industry continues to be lumbered with orifice dampers that do the above.
    www.dougal.co.nz Suspension setup & tuning.
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  15. #15
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    Quote Originally Posted by Dougal View Post
    The bike industry continues to be lumbered with orifice dampers that do the above.
    We can thank Marzocchi for that!!

  16. #16
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    ok DG, now that you saw some suspension velocity data, what are you planning to do with it?
    Normally, I would ask this question of Push, but I figure they won't want to give out their secret sauce recipes.

  17. #17
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    Quote Originally Posted by RecceDG View Post

    I'd love to see some MTB suspension data. Does anybody have any?
    yes

    Can you say 150 ips?


  18. #18
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    Awesome! Is that really from a handlebar smack like the image file name suggests?!?

  19. #19
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    All dampers are speed-sensitive? Your world has much better suspension than mine. Orifice-tube is more common here.

  20. #20
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    Quote Originally Posted by tyrebyter View Post
    All dampers are speed-sensitive? Your world has much better suspension than mine. Orifice-tube is more common here.
    Awww... come on...

    As explained before, all dampers are speed sensitive in strict theory as they change damping and behaviour according to shaft speed.

    However, it's a given that the term "speed sensitive" is applied to dampers that change orifice size according to shaft speed (either by shims, poppet valves, etc.)

    Let's get back to discuss expected shaft speeds, please instead on fruitless discussion about terminology... which sometimes is unique to bike industry as the same thing may be called something else in other industries.
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  21. #21
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    That "handlebarsmack" file was me forcing a hard landing to flat, which I think is one of the higher IPS events. The reason is that hitting a flat surface maximizes the spring constant of the tire, as opposed to hitting a sharp object that pinches the tire inwards. Here is some other token data and speeds:

    Ramming a 2" curb - 50 ips
    slowly dropping off a 6" curb: 50 ips
    flying off a 6" curb: 70 ips
    standing and mashing (pedal bob): 5-10 ips

    braking and swerving:


    Just Riding Along a smooth trail


    Concrete rock garden, maybe 1-2" roughness
    compression 3 clicks underdamped:


    my usual setting:


    3 clicks overdamped:


    velocity histograms:


    Minor comments for now:
    In the JRA data you can see the horrible horrible stiction in my Minute Pro fork, where the velocity likes to go to zero between little compression and rebound strokes.

    The velocity histograms are statistics for how much time the fork spends at each velocity. So for example, if you have too much compression damping, the fork never gets a chance to reach high speeds. It is some technique from 4 wheeled motorsports which is supposed to help set your damping. I don't know that much about them, but my guess is that you are aiming for a symmetrical histogram which somehow implies that the wheel is tracking well over bumps.

    This is my baller data logging setup.
    Last edited by beanbag; 12-02-2012 at 04:39 AM.

  22. #22
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    OK. I'm probably like the ape in Space Odyssey staring at the obelisk, but that is the coolest thing I've seen in a long time. What is it, what does it interface to, and where did you get it?

  23. #23
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    Yeah more info on your set up please. I have been considering buying an arduino and accelerometer (along with some other sensors) to play with on my bike - a goal of eventually setting up a cheap data logger for suspension data.

    Got any tips?

  24. #24
    PMK
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    Beanbag, some of our previous topics / posts I thought you were of the opinion that there was not much need for more than 50 IPS information.

    Not specific to Beanbag but everyone.
    The capability to constantly log IPS and dyno runs to at least a max of 150 is not stuff I made up. I still laugh when a shop flaunts they use a dyno of 20 IPS to build and test shim stacks and the sheep follow drinking Kool Aid along the way.

    The other part of the dyno puzzle that you must have to validate any working data is force. You can have huge IPS capability but if the dyno stalls at real world force values you will never see the true IPS.

    Here in lies the problem, how do you also gather force data? Consider also, forks are easy at a 1:1 leverage rate, rears are more difficult on account of instantaneous leverage rates. Force calculations based solely on measured weight are moot also in that you encounter weight bias constantly changing.

    Dynos and all the engineering is really cool and makes things look impressive but in the end, It still comes down to the setup needs to be ridden... and unfortunately each rider and terrain is uniquely different. So really it is nothing more than a best compromise, provided the rider is capable of offering up good feedback to make changes for the better.

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

  25. #25
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    Quote Originally Posted by PMK View Post
    Beanbag, some of our previous topics / posts I thought you were of the opinion that there was not much need for more than 50 IPS information.
    I am still of the opinion that the dyno does not need to go over 50 ips, for a couple of reasons:
    The rebound will never see more than 50 (or so) ips.
    The compression curves you can extrapolate out

    It's not worth 4x the money to get 2x more speed for 5% more information value

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