More daft musings really, but I'm needing to remove some air from my fork and shock - probably a very small amount as having ridden some slightly lumpier stuff faster then I normally do (looking ahead and getting lower with knees out really do make an improved difference!), I've noticed I'm about a 1cm difference away from full travel on both units.
I'll remove a measly 3psi from fork and 5psi from shock but whilst I was thinking that I was wondering why we don't sit on the bike to inflate fork or shock to set initial sag?
I don't know and suspect it'll be dead obvious when answered, but asking as I don't know other than I've never done that. Being on holiday, I'm clearly lacking some social interaction to stop me needing to think of these daft questions.
Air chambers need balancing, the balance port is normally quite close to full extension, therefore you've got to fully unweight the bike. Easier to do this off the bike.
Your adding another variable by increasing the pressure depending on the position you are on the bike, how heavy you are at the time etc. more weight applied will increase pressure so offsetting your required pressure, so unless you are adding based on the pressure increase from a reference (balanced and full extension or a repeatable measure of sag ) you'll never know your starting point reference.
Easier to pump up a at a lower pressure.
I have to say at this point - why has the specialized / fox auto sag thing not taken off more? It's brilliant to set a baseline setting from.
I remember my Magura Menja set up guide. Saying that the pressure was dependent on the type of riding and terrain and it gave a strict warning that if you didn't achieve maximum travel on any ride you weren't having as much fun as you should have.
The Fox/Specialized auto-sag was a kinda random approximate by-product of having an equalisation port. Not bad for ballpark, perhaps but not universal and if you start optimising design to make auto-sag work you might end up compromising the size balance of your pos and neg chambers.
Releasing pressure on the negative chamber (how auto-sag worked) meant you got the full positive pressure stressing the seals across the equalisation port; we're used to equalising every 50psi as we're pumping up a shock and seal design/robustness may be another area where auto-sag would introduce compromise.
Just musings. No facts.
I'd just leave it.
“I’ll remove a measly 3psi from fork and 5psi from shock”
Bear in mind that the pressure in them both is greater before you connect the pump - once connected the high pressure air will rush out and charge the pump hose etc, lowering the pressure in the shock and fork. If you then let out another 5 psi you’ll be lowering the pressure even more.
Unless you are a professional rider you probably wont even notice a 3 psi difference. I don't think it is even possible to be that accurate with the psi in shocks with your average shock pump. Would aim for around a + or - 10 psi accuracy at best. Any more and you are picking at straws.
There's a real obsession amongst some with making sure all travel is used. My view is that it's good to have some in reserve. Yeah, to may not use it on that ride when you ride it that way, but if you cock up and come up short, take a different line, hit something faster etc etc you may find you need it.
I'm an advocate of the 'set it up for most conditions and stick with it' approach.
Just because you're not maxing out it doesn't mean your setup is wrong. More sag could well turn it into a horrible wallowy mess.
If I bottomed out my bike on the ride I did yesterday along mostly smooth trails and bridleweays I'd be firming it up for sure.
“Unless you are a professional rider you probably wont even notice a 3 psi difference. I don’t think it is even possible to be that accurate with the psi in shocks with your average shock pump. Would aim for around a + or – 10 psi accuracy at best.”
I wouldn’t expect to be able to get brilliant readings with some shock pumps but I can certainly feel quite small differences. Last week I was tweaking my suspension after a service and after getting into the right window of about 5psi on the fork and 10psi on the shock the finest adjustments were literally just connecting and disconnecting the pump to let out a tiny amount of air.
I wouldn’t set suspension based on expecting to reach full travel frequently, there’s a lot more to it than that - how the bike feels and sits at sag, how it feels over rough stuff, what happens as you pump and preload and hop, what happens when you land bigger stuff, etc etc. Full travel on the shock is fairly common for me but not on the fork, but it’s usually from flatter landings on drops, not jumps with transitions (although much as I like getting airborne frequently I don’t have the confidence to go high/far).
I agree with the above...
In an xc pootle I'll use 120mm of my 160mm fork..
Will I use lower pressure next time.. NOPE!
Because there weren't big bits to bottom out on!
Set sag once, in the garage.. then adjust the compression and rebound...
If sag is correct, all else works from there...
DrP
Couldn't do it on my forks. You charge the positive chamber, then push a button on the bottom of the forks to equalize pressure in the negative. If you've got any weight on the bike, you'll just push all the air into the negative chamber and set the travel to zero.
Also, you kinda need to remove the pump or else you'll be wiring with an artificially big +ve chamber (fork PLUS pump and hose volume)
DrP