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Trying to dial in my dual air, but noticed that if the air pressure is low, but within the recommended range, you lose travel. I like to put in about 85-90 on both the negative and positive air which should hold for my light weight. But I can only extend the travel to 125 max. Is this happening to anyone else? I also noticed that to get more travel, I need more positive air. Why?
 

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Hmm

I used to run a Psylo Race gold the dual air version. From my understanding the positive air controled your preload , You set it to your weight as a main spring. and the negative controlled your rebound, How fast it would go to your full travel. You want more pressure on the positive chamber to extend the fork to your full travel. Setting them with the same pressure would cancel out the suspension effect making it set in mid travel. You should read the manual. You should have a higher persentage of pressure in the positive chamber. I do not have my manual anymore but I beleive you should set your positive air to you weight. and the negative chamber should be somewhere between %30 to %50 of the positive pressure (depending on how you like it). I think Marzochi Marathon forks have a system where you can adjust the travel by equalizing the air chambers but I think they also have a steel spring in the other leg. I beleive the Rock shok dual air have a oil dampening system in the other leg. Either way read your manual or download one on the rock shox web site they expalin it there better than I am able to.
 

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Man

them manuals are dificult to understand It looks like there is three versions of the pike A U-turn, a dual air (non adjustable travel0 and a U-turn air. I take it that you have a Uturn air. It looks like I am wrong about the negative pressure. they can be set equal or to about %80 of the positive. pressure. It does not specify if that is true for the U turn air. I looks like Uturn air has a spring and dual air chamber. It souns like the Marz Marathon forks that use air pressure to set the travel. But then you have a Uturn adjustment. If you can't find help here try SRAM drop an email or call the hotline.
 

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lchu80 said:
Trying to dial in my dual air, but noticed that if the air pressure is low, but within the recommended range, you lose travel. I like to put in about 85-90 on both the negative and positive air which should hold for my light weight. But I can only extend the travel to 125 max. Is this happening to anyone else? I also noticed that to get more travel, I need more positive air. Why?
You seem to have too much negative pressure or too little positive pressure.

Unfortunately the RockShox manual and website are wrong on what the negative pressure does, and the guideline pressures are just like any guideline... just a guideline.

Just ask yourself if you want the fork firmer or softer, and if you want more or less sag. Then:

EITHER

Consider the positive pressure your spring adjuster (higher=firmer), and the negative pressure your sag adjuster (higher=more).

OR

Consider the positive pressure your sag adjuster (higher=less), and the negative pressure your spring adjuster (higher=firmer).

Both methods give the same result and the setup you want, for any dual air fork (RockShox, Marzocchi, non-U-Turn, U-Turn, etc).
 

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I think you meant...

anden said:
You seem to have too much negative pressure or too little positive pressure.

Unfortunately the RockShox manual and website are wrong on what the negative pressure does, and the guideline pressures are just like any guideline... just a guideline.

Just ask yourself if you want the fork firmer or softer, and if you want more or less sag. Then:

EITHER

Consider the positive pressure your spring adjuster (higher=firmer), and the negative pressure your sag adjuster (higher=more).

OR

Consider the positive pressure your sag adjuster (higher=less), and the negative pressure your spring adjuster (higher=firmer).

Both methods give the same result and the setup you want, for any dual air fork (RockShox, Marzocchi, non-U-Turn, U-Turn, etc).
...and the negative pressure your spring adjuster (higher=SOFTER)

Right? At least, at the beginning of the travel? I'm currently playing with Revelation U-Turn adjustment.
 

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swoodbrn said:
...and the negative pressure your spring adjuster (higher=SOFTER)

Right? At least, at the beginning of the travel? I'm currently playing with Revelation U-Turn adjustment.
No. Higher=firmer. At the entire travel. And that's what the guys behind the RockShox website and manual haven't understood.

The negative pressure pushes down the fork to a more compressed position, while the bottom position force is still about the same. Thus, you have shorter travel going to the same end position force, and a steeper spring curve.

Try for yourself completely emptying the negative chamber (so that you get maximum positive travel and bad top-out hits), and see if the fork gets softer or firmer. If you are then still not convinced, try pumping it up to a huge pressure, and see how it feels.

Great fork with a misleading manual.
 

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I'll definitely have to try that, because it's totally nonsensical to me. Seems like the positive and negative pressures should be creating diametrically opposed forces (pos pushing down - trav extend, neg pushing up - trav compress). If that were the case, the RS explanation would make sense - more neg pressure yields more small bump sensitivity, b/c the shock would have greater propensity to compress. Clearly, I'm wrong, because then increasing pos would do same as decreasing neg (and vice versa), and there'd be no reason to have both.
 

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swoodbrn said:
I'll definitely have to try that, because it's totally nonsensical to me. Seems like the positive and negative pressures should be creating diametrically opposed forces (pos pushing down - trav extend, neg pushing up - trav compress). If that were the case, the RS explanation would make sense - more neg pressure yields more small bump sensitivity, b/c the shock would have greater propensity to compress. Clearly, I'm wrong, because then increasing pos would do same as decreasing neg (and vice versa), and there'd be no reason to have both.
The fork would not have greater propensity to compress, because with a higher negative pressure you will also have a correspondingly higher positive pressure at sag. The fork would just find a new (lower) equilibrium (sag) position, but with two higher pressures. And with such, it's harder to get it moving.

Marzocchi used to be wrong too, but they have now seen the light (I did the underlining):

2005 Bomber manual on negative air (p 118):
"By increasing the pressure inside the fork's leg, you increase the force helping the fork to start sliding."

2006 Bomber manual on negative air (p 141):
"By increasing the pressure inside the fork's leg, you increase the force required for the fork to start sliding."
 

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Nicely researched. Cite me a relevant bible verse and I might understand. So, if I want it to ride as high as possible (fullest travel, little sag), be pretty firm (no diving and such), but have good small bump sensitivity, I'd set: pos on the high side, neg on the low side. Tell me I'm right.
 

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Psylo Travel

You need to take all the neg air out of the fork. Now check you pos pressure again. You will notice a decrease in pressure. This is good. Now put the pressure you want in your positive chamber first (Always first!) . It is best to go at 20% sag of the travel for the fork to perform best. Now do the negative chamber to the same pressure if you want the fork to work right. This will take the stiction out of your system and give you small bump sensitivity. A little more will make the fork softer in the beginning of travel and the reverse if you have less neg pressure.

If this does not fix you problem then contact Rock Shox the guys there are super helpful.

Dont forget to always do the positive chamber first. If you pressurize the negative chamber first you will decrease you travel.

Ride!!!
 

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This system is not like Marzocchi because it uses the same chamber for air with a pison in between.

I forgot to mention that I have gone to SRAM Tec University's 4 day course.

Ride!!!
 

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swoodbrn said:
Nicely researched. Cite me a relevant bible verse and I might understand. So, if I want it to ride as high as possible (fullest travel, little sag), be pretty firm (no diving and such), but have good small bump sensitivity, I'd set: pos on the high side, neg on the low side. Tell me I'm right.
A firm spring gives worse small bump sensitivity, and a soft gives better small bump sensitivity. You cannot have a firm spring with good small bump sensitivity, or a soft spring with bad small bump sensitivity. It's a compromise.

It's hard to comment on pressures on high or low side, since we all are different weight, sit differently, and have different preferences. Also, absolute pressures depend on chosen spring rate. For example, a given rider may get the same sag with pos/neg 140/120, 100/100, and 55/80, but different spring rates.

I would recommend the method I described in my first post in this thread.
 

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weberbike said:
This will take the stiction out of your system and give you small bump sensitivity. A little more will make the fork softer in the beginning of travel and the reverse if you have less neg pressure.
Because someone at RockShox said so?

weberbike said:
This system is not like Marzocchi because it uses the same chamber for air with a pison in between.
I think the Marzocchi system is the same principle, because that's the obvious way for a dual air spring to work - one main spring and one counteracting negative travel spring. The pressure effects also support that assumption. See below how I think the Marzocchi system looks. The RockShox one is shown for comparison. What makes you think the Marzocchi system is different, or even better, how does it look?
 

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Well, isn't that the whole intent of all this Motion control, and positive and negative pressure technology - to try to achieve good big AND small bump handling?
 

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I do believe that anden has this wrong. The more neg pressure compared to positive the more supple the fork will bein the first inch or so of travel. After this point the neg chamber increases in size and so the pressure drops whereas the pos decrease in size and so the pressure increases. This means that the contribution of the neg to the ride of the fork is reduced as you move through the travel.

I have played with this on my pike dual air u-turn. If i have 100 in pos and 80in neg then it is nice, if i up the neg to 120 then it more supple and really eats the small bumps but you lose a couple of mills of travel when you unload the fork.

Stuart
 

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anden said:
Because someone at RockShox said so?

I think the Marzocchi system is the same principle, because that's the obvious way for a dual air spring to work - one main spring and one counteracting negative travel spring. The pressure effects also support that assumption. See below how I think the Marzocchi system looks. The RockShox one is shown for comparison. What makes you think the Marzocchi system is different, or even better, how does it look?
Ain't that simple with the Zoke... There are three separate chambers. One for positive which is the whole leg, minus oil and cartridge volume.

Then there's the cartridge that holds two chambers inside, divided by a single piston. The upper one is the negative air and the lowest one is the PAR.

The volume on the negative side is lower than the Positive counterpart. So that's why you find that in a Zoke you need like three times the pressure on the neg, compared to the pos.

smh151 has it right. The more pressure you have in the neg, it will make it much more better compliant in the initial part of the travel... and eventually reduce the travel if pumped too high. As the neg pressure chamber increases it's volume, it's contribution is neglected and you get to the point where you are actually fighting against the PAR chamber pressure, which sums to the pos chamber pressure to prevent bottom out. Too high par and you'll be using even less travel.

I ignore how is the RS system, though.
 

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swoodbrn said:
Well, isn't that the whole intent of all this Motion control, and positive and negative pressure technology - to try to achieve good big AND small bump handling?
It sure can handle overall good. But you can't get everything maximized at the same time. You have to compromise, even with the world's best forks.

There are natural contradictions between plushness and stability, between small bump compliance and anti-bobbing, between off-road comfort and anti-diving. No TST, Motion Control, Doppio Air, negative pressure, Floodgate, or PAR can change that.
 

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smh151 said:
I do believe that anden has this wrong. The more neg pressure compared to positive the more supple the fork will bein the first inch or so of travel. After this point the neg chamber increases in size and so the pressure drops whereas the pos decrease in size and so the pressure increases. This means that the contribution of the neg to the ride of the fork is reduced as you move through the travel.

I have played with this on my pike dual air u-turn. If i have 100 in pos and 80in neg then it is nice, if i up the neg to 120 then it more supple and really eats the small bumps but you lose a couple of mills of travel when you unload the fork.

Stuart
You seem to be missing that as you increase the negative pressure, it pushes down the fork and increases the positive pressure correspondingly much. It's not like you pump up a potential that waits for you to hit a rock and only then explode to compress the fork. You will at sag still have the same relation between the positive and negative pressure. The only difference will be that the fork sits lower and that both pressures are higher. And with higher pressures, it is harder to compress it further.

The firmness has more to do with how much total air you have pumped into the leg. More=firmer, no matter where you pump it in. Sag, on the other hand, is determined by where you pumped it in.
 

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Warp2003 said:
Ain't that simple with the Zoke... There are three separate chambers. One for positive which is the whole leg, minus oil and cartridge volume.

Then there's the cartridge that holds two chambers inside, divided by a single piston. The upper one is the negative air and the lowest one is the PAR.

The volume on the negative side is lower than the Positive counterpart. So that's why you find that in a Zoke you need like three times the pressure on the neg, compared to the pos.

smh151 has it right. The more pressure you have in the neg, it will make it much more better compliant in the initial part of the travel... and eventually reduce the travel if pumped too high. As the neg pressure chamber increases it's volume, it's contribution is neglected and you get to the point where you are actually fighting against the PAR chamber pressure, which sums to the pos chamber pressure to prevent bottom out. Too high par and you'll be using even less travel.

I ignore how is the RS system, though.
Yes, the design is functional. Though, it seems that you may be understanding the sketch slightly differently from what I intended with it. I realize it's unclear and uncomplete. The positive chamber is only the upper half of the leg. Under that, there is a piston head that is attached to a rod being attached to the leg's bottom and going through the bottom of the stanchion. The rod is hollow and perforated at the upper and lower part. Not that there's much functional difference to how you saw it.

Regarding the negative pressure, see my reply to smh.
 

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anden said:
Yes, the design is functional. Though, it seems that you may be understanding the sketch slightly differently from what I intended with it. I realize it's unclear and uncomplete. The positive chamber is only the upper half of the leg. Under that, there is a piston head that is attached to a rod being attached to the leg's bottom and going through the bottom of the stanchion. The rod is hollow and perforated at the upper and lower part. Not that there's much functional difference to how you saw it.

Regarding the negative pressure, see my reply to smh.
I was describing a REAL Doppio Air cartridge... not your sketch.

I have seen a picture of it opened. It's different to what you describe.

See my reply. The neg and PAR share a canister with two chambers. The positive is the whole leg minus the volume of the cart and oil.

My comments on neg pressure remain... your comments describe an obvious consequence. That's why they give you max an minumim pressures... so no one get creative enuough to "firm up" a fork while still getting it small bump compliant. Seems like a recipe for blown seals.
 
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