Rockshox Reba negative pressure

muzzle1
muzzle1 Posts: 21
edited May 2012 in MTB workshop & tech
Hello all, last question on my new Rebas (I hope!).

I've set positive and negative pressures to 100psi to start with. Every time I attach the shock pump again, the positive pressure is pretty much where I left it when I last removed the pump, whereas the negative pressure seems to have dropped every time. Is that just because a little bit of air loss from reattaching the pump is magnified in the negative because of the much smaller air volume?

For what its worth, I've left the pump attached to the negative for some time and the pressure hasn't fallen on the gauge while I've been watching it, and yet I can remove the pump and immediately reattach it and the pressure has dropped by around 20psi in no time.

If I'm correct in my assumption, is it safe to assume that the pressure is lost on reattachment rather than when I'm removing the pump? If the former, no problem; if the latter then it's obviously a concern if my forks are not at the pressure I've set them.

I'm reasonably sure there's nothing to worry about or any fault, but if anyone can reassure me (or indeed tell me there IS a problem) I'd appreciate it.

Thanks.

Comments

  • cooldad
    cooldad Posts: 32,599
    Yes and yes. Don't worry.
    I don't do smileys.

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  • sensi10
    sensi10 Posts: 68
    I have 2012 reba rlt and they do the same thing. I was really worried at first and thought there was something wrong but Ive come to understand that the negative side is much smaller than the positive side.
  • Plyphon
    Plyphon Posts: 433
    muzzle1 wrote:

    For what its worth, I've left the pump attached to the negative for some time and the pressure hasn't fallen on the gauge while I've been watching it, and yet I can remove the pump and immediately reattach it and the pressure has dropped by around 20psi in no time.

    Your assumption is correct - this pressure is lost because the air has to fill the pump again. Effectively the area you are measuring the pounds per square inch is increased, but with the same volume of air, so the PSI decreases. :)
  • muzzle1
    muzzle1 Posts: 21
    Ah, makes sense. Thanks everyone.
  • nicklouse
    nicklouse Posts: 50,675
    As covered in the FAQs.

    Seriously have a look through them.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
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