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  1. #1
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    SB95 RP23 Air Volume Spacer

    I've been playing with different size Fox air volume spacers and have managed to confuse myself.
    I weigh 165 geared up. When I set the stock shock sag to 28% I bottom out the shock many times during a ride which includes a lot of ~1ft downhill steps and several ~3ft to flat drops. When I add the 0.2 CuIn spacer it bottoms just as much, but maybe a little softer. The 0.4 CuIn spacer helps a lot, but the over all ride gets a bit weird -- a little harsher and much less stable. Adding more rebound dampening helps the stability, but makes rebound very slow in the first half of travel.
    Any thoughts?

  2. #2
    Spring! Spring! Spring!
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    I dunno, on my RP23 I only needed to put in the smallest spacer to get good bottom-out handling, and I usually ran it around 28-30%. BUT, I weight a bunch more than you (~220 geared up) and had to probably run a bunch more PSI, which would make a big difference.

    Hopefully someone of like size will be able to comment.

  3. #3
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    Quote Originally Posted by Torque Wrench View Post
    .... and several ~3ft to flat drops....

    there is your answer. If you have a spring that handles that, it's going to be harsh on smaller stuff. To get your shock to do what you want, it's going to take some internal adjustments; like more high speed damping or maybe more boost valve/IFP pressure.
    The bigger wheels slow the shock accelerations when hitting bumps, but not when dropping.

    typically, it's heavier riders that need reduced spring volume.

  4. #4
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    Thanks Bear. Maybe weight makes a difference.

  5. #5
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    Thanks Joules. You mean I have to compromise and can't have it all ?
    Quote Originally Posted by Joules View Post
    there is your answer. If you have a spring that handles that, it's going to be harsh on smaller stuff. To get your shock to do what you want, it's going to take some internal adjustments; like more high speed damping or maybe more boost valve/IFP pressure.
    The bigger wheels slow the shock accelerations when hitting bumps, but not when dropping.

    typically, it's heavier riders that need reduced spring volume.

  6. #6
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    Quote Originally Posted by Torque Wrench View Post
    Thanks Joules. You mean I have to compromise and can't have it all ?
    only way imho to have it all is to send to someone like Push and have it custom tuned...money well spent imho

  7. #7
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    Quote Originally Posted by Torque Wrench View Post
    Thanks Joules. You mean I have to compromise and can't have it all ?
    Not necessarily, just that the 3 external adjustments on a rp23 don't control the things you need to mess with. Not saying you should run out and get a different shock, but I'd bet if you had a DBA or x-fusion vector air (which has high and lsc, ifp pressure and volume adjustments) you'd be able to find a combo that does what you want.
    Push or suspension experts or some other suspension tuning service could probably make your RP do what you want.

  8. #8
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    Bear nailed it right on the head , since he is bigger he takes more initial air pressure and it ramps that pressure up, and with one volume spacer thats all it took to dial him in.

    You and I on the other hand ( I am 165 with all my gear and water on also ) start with a lower pressure and even with added spacers it will not not ramp up enough to stop it from bottoming ,.......but it will however become very harsh on small bump stuff ( especially if you have a BV shock , that boost valve actually really sucks in many ways ).

    I had the same problem , I could make a .8 Volume spacer kinda work with 140 psi of air .....but I would still bottom all the time.

    Like was said here in several posts , you need to have internal valving altered and remove the boost valve , and add a high flow piston and re-valve it and you will love the thing

    Like was said earlier in this post send it to push and you will be amazed

  9. #9
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    I'm the same size as you but have the CTD LV shock. How hard is it bottoming? It always uses full travel even on easier rides but I only feel it bottom on bigger 3' plus drops to flat or harsh transitions. Bottoming isn't a bad thing necessarily. Are you running it open? The hits you describe are more lsc than hsc and putting the shock in the stiffest pro pedal setting will help. Short of a complete custom tune, increasing the boost valve tune (ifp pressure) 10-20 psi will create a descent bump in the overall damping. Sounds like you could really benefit from a reb revalve. That is the best thing I've done to my shock. I've also replaced the bv with a shim stack but haven't quite got it dialed yet.

    Sent from my A500 using Tapatalk

  10. #10
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    And most importantly, what I forgot to say is that bottoming is more a function of spring rate than damping.

  11. #11
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    Thanks for all of the responses everyone. The dampening feels pretty good in general and soaks up the high speed square edge stuff. It doesn't bottom out super hard with the 0.2 CuIn spacer, just enough to feel a slight jolt. As mentioned PUSH is a good option, but maybe this is a non-issue if my teeth don't get rattled when I land?

  12. #12
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    Check out the compression ratio chart for the CTD shocks.

    WebHelp >Quick Tech: Rear Shocks >Float 2013 CTD

    My shock is the LV with a .4^3in spacer in it, came stock that way. I'm not 100% sure, but I think your RP is equivalent to the SV, in which case Fox doesn't even recommend running any spacers. So, the LV with a .4 spacer is 2.7 comp ratio versus the SV with no spacer is 3.6 comp ratio.

    What is your complete setup? Fork model, air, rebound, lsc and shock air, rebound, lsc. If your fork is out of balance with the shock, over damped or sprung, it can cause excessive shock bottoming and a poor ride in general.

    I would remove the spacer and set your sag at 25%. A higher spring volume will actually provide better midstroke support. The boost valve shocks are already bad about blowing through the midstroke which doesn't help with bottoming. Like you've noted, when the comp ratio of the spring gets high, the shock starts riding weird mostly due to the reb damping curve not matching the spring curve but also because it ramps up too early in the stroke.

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