Hello,
Just away out on a cheeky ride, what a day btw, thought I’d stick up something that has been stewing away for a while- my pikes lose quite a bit of air pressure over the course of a ride… Pump them up to ~130 psi and by the time I get back they’re sitting ~70.
Is there anything I can do to try and resolve this myself, ie tighten the bottom valve? or is a service the way forward? Don’t want to lose the use of the bike for a few weeks right now! 🙁

Many thanks, Calum

mine does that too, someone suggested it was a leaking valve core in the -ive air chamber. I keep meaning to get hold of a valve core removal tool thingummyjig but haven’t managed it yet so I just check the pressures regularly and adjust as required

How do you know that they are at ~70 when you get back from a ride?

The -ve chamber is a lot smaller than the +ve so if you are fitting your pump on the -ve to check the pressure, then that is where the discrepancy lies. Fitting the pump increases the volume (proportionally) by a lot and so drops the pressure.
On the +ve side, the volume increase isnt’ so great as a proportion, so the pressure change isn’t so significant.

Stumpy, interesting, I remember reading something like this before albeit about another issue…
The forks do seem to be softer after a few hours… Going to try an experiment with a pump now to see what effect disconnecting/reconnecting has…
Thanks for the advice so far….

Ok, so pressure registered 85(ish) on connection, inflated to 130, disconnected, reconnected, pressure registered 100.
Hummmmmmmmm. Maybe I don’t have as big a problem as I 1st thought?

As Stumpy says, when you connect the pump, air from the fork chamber expands into the pump. Since the -ve chamber is a very small volume, this leakage has a large impact on pressure.

When you disconnect, however, the pressure loss you hear is from the pump, not the fork.

Therefore every time you check you get a false reading.

The only way to check for a leak in this way is to see if the loss is repeatable – i.e. do you always read 80psi, or after a ride and a week is it 60psi?

Also – if the -ve air is leaking, the fork would feel firmer due to loss of -ve spring, not softer.

Stumpy et al, the milky bars are on me. Problem(or lack thereof) solved.
Many thanks. 🙂