Rock Shox dual-air systems

The ‘blurb on the fork legs tells me to balance the pressure equally in both pos and neg air chambers. I’ve a set of Reba’s (2007) and a set of Pikes (2009) and both sets of forks will suck down the travel if i attempt that, they both seem to need about 15-20psi less in the negative chamber to return the fork to full travel after a series of hits, problem with that of course is they then tend to be a little harsh over small bumps.
Is it me or anyone else have the same problem?

Pikes are at J-Tech at the moment for a service, mentioned this to them and hopefully they can solve it.

I have some new Sid RCT3s and they are the same.

I run my Revs 20psi lower in the negative chamber. The more pressure you have in the negative chamber the easier it is to initiate travel. It’s a fine balancing act.

Design then? Oh well…

Also the negative chamber is small making it harder to fine tune.

Weird that: on mine they are fine with both pressures the same or – slightly higher. Maybe I’m not “hitting” them hard enough.

Think that’s whay Rockshox have abandoned the dual air system for next (this?) year’s forks. Think I’ve read that anyway.

Sometimes i get it ‘just so’ then the next ride it feels all wrong again.
On the Pikes i find that the forks do lose about 5mm (yeah, i know) of travel even when set up as best as i can get them, most of the time its about 10 mm packing down.

Anyone have the Solo versions? they automatically equalise i believe so i wonder if they too pack down?

That’s the way they work, my 2012 rebas probably lose about 10-15% of travel with my normal setup of about 5-10psi extra in neg, but it’s the small bump compliance I want out of them for most riding. A quick tweak changes that when it gets rougher/bigger, I really like the system but do find it a bit hit an miss sometimes (but that’s mainly cos I don’t know what i’m doing…)

Also slightly lower in neg. Might be to do with accuracy of the pump and the relative sizes of the chambers?

I have some 2008 rebas. Removed the travel spacer to achieve 115mm. Run them with 6-8 psi less in the neg and find im getting 117mm travel.

Make sure you let all the air out the neg chamber first. Then pump the pos chamber before the neg.

Remember to fill + THEN – to the same amount starting with both empty( to Say 100psi), they should work without a reduction in travel. If you were to check both at that point the + would read higher than the -, which is normal. My dual air pikes and revs only reduced in travel if a) they were borked or b) I’d played with air pressures without starting from empty.

Yep, same with my 2008 revs. However it works great for me as I want 120mm travel out of my 130mm forks with great small bump compliance.

10-15 less psi in the neg is the standard in my experience.

It’s not *actually* possible to run higher pressure in the negative chamber than the positive, since they’re in equilibrium – As soon as the pressure in the negative chamber is greater than the positive side, the fork will get ‘sucked’ down, the positive air chamber decreases in size and the positive pressure therefore increases to match the negative pressure.

So yeah, if you put in more volume in the negative side, it’ll suck the fork down. But it should be possible to match the pressures without losing any travel.

It all becomes a bit moot as soon as sag becomes involved though.