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Rear kicks or bounces up when hitting things at high speed?

Discussion in 'Downhill & Freeride' started by Dh builder, Jun 3, 2014.

  1. Dh builder

    Dh builder Chimp

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    Looking for some advice on what to adjust when the rear kicks up when hitting things at high speed. Stuff like 3 or 4" curb will really bounce the rear up while the front is just fine.

    I am not sure what could be the problem.

    What seemed to help so far was lowering the air pressure in the rear tire. The rebound is at a very slow setting.

    I am not sure if maybe the rear shock is bottoming out and bouncing me up, I just don't know.

    I have a FOX DHX RC4 rear shock.

    Thanks for any advice on what to adjust.
     
    #1 -   Jun 3, 2014

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  2. cowman

    cowman Monkey

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    First, I'd start with the basics. Do you have the proper spring rate (~30% sag)? Is the pressure in the boost valve in the proper range (~150 psi)? What bike is this on?

    If those things are correct, and since you stated your rebound is already slow, the only thing I can think of is you could be feeling a compression spike. Where are your compression settings? Backing off the high speed compression adjuster could help with the 'kick' you're experiencing.

    If none of the above things help, you could have a blown shock... Does it have any dead play at the top of the stroke? I've found that to be somewhat common on well used RC4's.

    Hope this helps!
     
    #2 -   Jun 3, 2014
    Last edited: Jun 3, 2014
  3. jonKranked

    jonKranked Press Button, Receive Stupid

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    did the bike suddenly start doing this? like, it started performing this way after a particularly large impact.
     
    #3 -   Jun 3, 2014
  4. big-ted

    big-ted Danced with A, attacked by C, fired by D.

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    Do you ride an Evil?







    Sorry. I had to....
     
    #4 -   Jun 3, 2014
  5. frorider

    frorider Monkey

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    the answer is always moar shimz
     
    #5 -   Jun 3, 2014
  6. jonKranked

    jonKranked Press Button, Receive Stupid

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    too many shimz? try moar shimz. eventually it will come full circle.
     
    #6 -   Jun 3, 2014
  7. OGRipper

    OGRipper Turbo Monkey

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    If your rebound is super slow, it could be that you are getting stuck down in your travel and don't have enough suspension available for successive hits, which can feel like "kicking". This is especially true if your front and rear suspension is not balanced.
     
    #7 -   Jun 3, 2014
  8. descente

    descente Monkey

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    x2 if the rebound is too slow and the bike is packing up, it'll give a similar feeling. basically, its hitting the spot where the spring rate and leverage ramp enough that it can't compress anymore (for the given input) and you get that kick back feeling even though you're not bottomed out.

    for what its worth, since you didn't mention it, but when i ran a Ti spring on my RC4 i could never get the rebound into an acceptable range compared to a steel spring (different materials have different rebound rates), this was especially noticeable on the type of hits you are describing.

    have you tried any different settings yet?
     
    #8 -   Jun 3, 2014
  9. Dh builder

    Dh builder Chimp

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    This is interesting, I wonder if this could be the case about being too far down in my travel. I especially noticed this problem after dropping off a curb and then quickly hitting another curb.

    I also think my spring rate is a little too low because I bottom out a lot on my bike, I also turned up my bottom out control really high to make up for this.

    Could it be possible that the too low spring rate, also with the bottom out control really turned up, could cause this problem?
     
    #9 -   Jun 4, 2014
  10. jonKranked

    jonKranked Press Button, Receive Stupid

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    very likely
     
  11. OGRipper

    OGRipper Turbo Monkey

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    If you have turned up your bottom out control and are still bottoming out a lot, it's almost certain you need a heavier spring. All of your problems are probably coming from that simple fact.

    You don't want to use shock settings to compensate for the wrong spring. So yes, the first step is always to make sure you have the right spring. But generally you do that by checking sag, not bottom-out.

    Note that even with the correct spring you should be able to adjust the shock to allow an occasional bottom out if that's your preference. People have different opinions on whether you should be bottoming out every run or less often, plus different bikes create different leverage curves. Once you have the right spring you can tune your shock for your bike and personal preference. But it starts with the right spring.

    We could probably help more if you tell us what bike, what spring you have now, how much you weigh, etc.
     
  12. descente

    descente Monkey

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    and it also depends on what trail you're riding. most of the trails i ride on a regular basis, if you're bottoming out on the regular you've probably got too soft of a setup.

    how much preload do you have cranked into that spring? which end of the psi spectrum are you at in the reservoir?
     
  13. DHDror

    DHDror Monkey

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    with all the (good) technical advise and tips you got here , maybe you are just leaning forward too much...
    try to lean backwards just a little as the speed goes up.
     
  14. Dh builder

    Dh builder Chimp

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    I replaced that rear shock with a 50lbs heavier spring and what a difference. You can actually feel the suspension progressively lower after each hit on hard terrain. It almost feels like cheating as you don't get bounced around.

    I had to lower my low speed control a lot with the heavier spring as it felt very stiff with the heavier spring.