# how to set up my new Pike 426 air U turn



## evil monkey (Jun 9, 2007)

so I got the pike recently and it is the first fork that allows me to "adjust". so I tried to pump up the air chamber according to the right PSI for my weight (150-155 lbs). After I let the existing air out and pumping in the new air from my pump to the PSI, I realize the travel of the fork shrunk!! i am sure its got something to do with the air pressure thingy. can someone help me figure out what to do? I pumped it to the right pressure....on both + and -...is it my pump??


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## snaky69 (Mar 8, 2005)

Is there a negative and a positive air chamber in that fork, I can't remember. If there is a negative air chamber and you pumped it up more than the positive, it will shrink.

Also, you may have played with the u-turn feature.

You should not have let all the original air out, there is no need to and I seem to recall emptying an air fork was a bad thing unless you were about to service it anyway.


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## Squash (Jul 20, 2003)

*There is absolutely nothing....*

wrong with letting all the air out of an air fork or shock. It does nothing to the fork or shock but allow it to collapse. evil monkey you are absolutely right, the "shrinkage" has to do with the air chamber. The air chamber in an air fork is the spring. With no air in the chamber or only a very small amount the fork has no spring in it basically. Most will collapse to some extent of their own weight if they're a good fork.

To set up the Pike air U-turn correctly there are three things you must do in the correct order. First, make sure that the U-turn is set to it's longest travel setting. If you intend to remvoe the air be sure that you deflate the negative chamber first, then the positive chamber. When you inflate make sure that you inflate the positive chamber first. Once the positive chamber is set where you want it. Pressurized the negative chamber. A rule of thumb with Rock Shox dual air forks is to never add more pressure in the negative chamber than what you have the positive chamber set at. The reason being is, if the - chamber is set higher than the + chamber it will not allow the fork to return to full extension or will cause the fork to settle into it's travel when at rest (no weight on the bike).

Go slow with your adjustments and make adjustments in small increments until you learn how each one affects the fork. There is allot of adjustability with the Pike + and - air pressure, rebound damping, compression damping, and the flood gate settings. Each one has a different purpose. With a little time and experimentation you'll find the settings that will work for you and the way you ride.

Good Dirt


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## evil monkey (Jun 9, 2007)

Squash said:


> wrong with letting all the air out of an air fork or shock. It does nothing to the fork or shock but allow it to collapse. evil monkey you are absolutely right, the "shrinkage" has to do with the air chamber. The air chamber in an air fork is the spring. With no air in the chamber or only a very small amount the fork has no spring in it basically. Most will collapse to some extent of their own weight if they're a good fork.
> 
> To set up the Pike air U-turn correctly there are three things you must do in the correct order. First, make sure that the U-turn is set to it's longest travel setting. If you intend to remvoe the air be sure that you deflate the negative chamber first, then the positive chamber. When you inflate make sure that you inflate the positive chamber first. Once the positive chamber is set where you want it. Pressurized the negative chamber. A rule of thumb with Rock Shox dual air forks is to never add more pressure in the negative chamber than what you have the positive chamber set at. The reason being is, if the - chamber is set higher than the + chamber it will not allow the fork to return to full extension or will cause the fork to settle into it's travel when at rest (no weight on the bike).
> 
> ...


thx so much Squash!!! I did the opposite!! I set up the negative chamber first then the positive. i shall do it again and see if things will change.

so is it really bad to empty the air? basically i was just "experimenting" when i was making the adjustments.


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## evil monkey (Jun 9, 2007)

there was a bit of oil leak while i was doing the pumping. no idea where it came from, it most likely came from the fork...is it a problem>??


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## evil monkey (Jun 9, 2007)

btw, something is weird with my pump. not sure how to put this but...

if i pump the air in. pressure shows 120. i take it out and put the pump in again to measure the pressure, it would drop by 40 at the negative end and about 10 at the positive end.

what does that say??? the air leaks during the process of attaching the pump to the valve? but then why would it drop by so much?

and what is the ideal pressure for someone who is 150-155?? i put it at 120, but i feel its a bit too hard.


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## Fogerson (Oct 16, 2007)

evil monkey said:


> btw, something is weird with my pump. not sure how to put this but...
> 
> if i pump the air in. pressure shows 120. i take it out and put the pump in again to measure the pressure, it would drop by 40 at the negative end and about 10 at the positive end.
> 
> ...


The drop in pressure is the air filling the hose, etc. of your pump. What you're seeing is normal.

I have a revelation 426, run 110-115 +, and I hit the scales at around 200 lbs (I don't do any big drops, btw). So at a buck-fifty 120 psi is certainly too much.The numbers rock shox recommends are notoriously high. Search the forum for revelation 426 setup threads and you'll find a lot of info on setting these forks up.

'Net is add/drop air until you have 25-30% sag. Ride. If you never bottom, remove 5 psi at a time until you do. If you bottom a lot, add 5 psi at a time 'til you don't. And, generally folks seem to run 5-10 psi less in the - than the +. I've found I prefer running the same in the negative.


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## Squash (Jul 20, 2003)

*No it is not a bad thing to...*

deflate the air chambers completely. Well you can't really do it completely you still have air in them no matter what you do, it just has no "pressure" other than normal atmospheric pressure. But it doesn't hurt the fork at all.

What you are experiencing with the pump is normal. It's basic physics. If you have a cylinder of a given volume and add a given volume of gas inside the cylinder the pressure inside the cylinder goes up. If the cylinder is increased in size but the volume of gas inside remains the same, the pressure of the gas inside goes down. This is basically what is happening when you re-attach the pump to your fork. The volume of the hose and and gauge of the pump is not pressurized. When you attach the pump and break the seal of the schrader valve of the air chamber, air rushes from the air chamber through the hose to the gauge and then registers on the gauge of the pump. The thing is the volume of the + chamber is rather small, and you've just added volume to that chamber with the hose and gauge. The added volume is enough to actaully decrease the pressure by 10 psi. So it appears that you've lost or leaked air. Well technically you have, but it went into the pump not just out into the atmosphere. The - chamber of the fork is very much smaller than the + chamber (about 1/4 of the volume) so the air that comes from it into the pump when you re-connect has a more pronounced effect. So it appears that you loose 40 psi when you connect to that chamber.

So if you had say 150psi in the + chamber and 140 in the - chamber when you last disconnected the pump that is what was in the chamber before you reconnected the pump. But when you reconnect to "check" the pressure it's always going to read 10 psi less for the positive and 40 psi less for the negative because of the added volume of the pump. So the chambers will read 140 and 100 psi respectively when you reconnect. And they will remain at that pressure should you disconnect without adding air back in to compensate.

Like I said it is perfectly normal. So keep it in mind and just do a little simple math each time you check the pressure in your fork, which you should do before every ride. You know what you left the chambers pressurized at the last time. Just add 10 for the positive and 40 for the negative reading that you get when you reconnect the pump. If it matches fairly closely what you left the fork at last time your good, just pump it back up to your desired setting and ride. If you start seeing much larger differences then you likely have a leak and something needs to be serviced or repaired. Also keep in mind that no seal is perfect. Any air fork or shock will loose a bit of pressure over time, it just shouldn't do it overnight or in the course of a single ride.

The bottom line is, your fork and pump are fine and exhibiting normal behaviour. :thumbsup:

As for the "ideal" pressure for your fork and you. That's something that you will have to figure out. The pressures that RS lists on the fork leg are starting/recommended pressure combinations for a given rider weight. From there it is up to you to "fine tune" the fork to you liking and needs. And don't forget that you can work both positive and negative pressures to give different feeling to the fork. So if you are at 120 positive and 120 negative and if feels to harsh, drop the + by 10 psi and the - by 20 psi and try that. If this is good, but the fork feels a bit harsh over small bumps add 10 to the -. Still to harsh, increase the - another 10, but don't exceed the pressure setting of the positive chamber or you'll start loosing travel. Just keep fiddling with it and don't be afraid to experiment. There just isn't a hard fast "ideal" pressure for a given rider weight, riding style, bike, and terrain combination. Even if you and I were the same weight riding the same terrain on identical bikes, what works for me likely wouldn't work for you. So anything you get from anyone else would simply be a "recommendation". Keep at it and you'll find your ideal set up for the fork. It can actually be allot of fun. Hit the trail and take the pump along. Make it a short loop so you can ride it repeatedly and make adjustments after each loop. That's the best way I know of to get to know your fork. That and read the owner's manual!

As for that tiny bit of oil, don't sweat it, it's not an issue and it's normal for most air forks. There is between 3 and 5 cc of oil in the chambers. This is to keep the piston seals lubricated. It's not uncommon for a bit of it to come out during air up operations, esspecially from the negative chamber because it is essentially upside down. If you do the routine maintenance that RS suggests in the owner's manual you will replenish the oil long before it's completely gone. So don't sweat it.

Good Dirt


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## evil monkey (Jun 9, 2007)

Squash said:


> So if you are at 120 positive and 120 negative and if feels to harsh, drop the + by 10 psi and the - by 20 psi and try that. If this is good, but the fork feels a bit harsh over small bumps add 10 to the -. Still to harsh, increase the - another 10,


hi Squash, thanks so much!!! i was getting quite frustrated with this bike cuz it felt so different than the bike i had before. and adjusting the forks/shox is suppose to be the simplest procedure out of the rest that i had to do (whobble wheel/rotor, maybe contanimated rotor, dereilleur alignments).....however, knowing there are people like you who are willing to spend time helping out newbies like me does make this process much more comforting. in fact, it is actually a relavation knowing/learning more about the bike as oppose to just ride it (my older fsr xc w/ 0 adjustments). so thanks agian! =)

btw, can you please elaborate on the quoted statement? i understand the - air chamber is for taking on small bumps along the way. the less air in the chamber, the more sensitive/reactive the fork is to the bumps? so what do u mean by "harsh"?? too hard? not reactive enough? if so, shouldn't I be dropping more pressure??

btw #2: when the fork is in LO position, does it lock up the + or - chamber? or both.


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## Squash (Jul 20, 2003)

*The negative chamber.....*

is actually right below the positive chamber. The piston for each is even on the same shaft. The positive chamber is the main spring of the fork. The negative chamber acts in the oposite direction of the positive chamber and against it. So the positive chamber trys to keep the fork at full extension, the negative chamber trys to compress the fork and it can do so if the pressure in the - chamber exceeds the pressure in the +. But the - is muc shorter and smaller than the + so this affect is limited. Anyway the idea behind it is that with early air forks it was discovered that because of the pressure exerted against the seals etc. by the air pressure that the forks felt sticky and didn't like to move the first few milimeters of their travel very well and that the felt harsh or hard in their first 1/4 or so of travel. Rock Shox answer to this was the dual air system. A smaller pressureized chamber that acts agains the negative chamber and allows the fork to move much more freely in it's initial travel. The more pressure you have in the negative chamber the more force it applies against the positive chamber, thus the easier it is for the fork to start the compression stroke and the more sensitive it is to small bumps etc. The beauty of the system is that it does this, if properly set up, without affecting sag, or bottoming out all the time due to to little air in the positive chamber. So to increase sensitivity to small bumps you would increase the pressure in the - chamber, to decrease the sensitivity, make the fork feel stiffer/harsher/harder you would decrease - pressure. This of course is assuming that the + chamber is properly set up for your weight, riding style, etc.

When the fork is locked out it locks out neither the + or - chamber. The lock out is not even related to that side of the fork, though it does affect it by locking the fork out. The lock out system is in the oposite leg and is accomplished though the damper. The lock out is hydraulic! What basically happens when you activate the lock out is you close off the compression damper. Years ago there used to be forks and shocks out there that used "mechanical" lock outs, that acted on the springs or other bits of the fork or shock to lock them out. But they were highly suseptable to damage, esspecially if you forgot to "unlock" after a climb and started taking big hits on the way down! Even some early hydraulic lock outs were suseptable to damage if you left them in the lock position and started taking hard hits. With a modern hydraulic lock out this is prevented by using a "blow off" system. In your case Rock Shox calls it the "Flood Gate", and it is adjustable. It's actaully pretty simple. When the lock out valve is activated it prevents oil from flowing through the compression damper, effectively locking out the fork. This valve is spring loaded so it can move if necessary though. The rate of the spring determines how much bump force is required to "blow" the valve open and allow the fork to compress. But it is always blows off at a level that will prevent damage to the fork. All the flood gate adjustment does is add a little additional pressure to the spring so that it takes more force to open the valve. Turning the Flood Gate knob to the + side increases the amount of force required to open the valve, turning it to the - side lessens the force required. So your lock out is custom tuneable as well. So the lock out acts on neither the positive or negative air chamber but on the damper in the other leg, and the blow off valve protects the fork from damage should you forget to "unlock" after a climb and start bombing the descent with the fork locked out.

Good Dirt


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## CharacterZero (May 19, 2004)

Just a heads up on actual PSI - most people have found that 50-60% of riding weight is good for breaking in the PIKE. Adjust according to how much you bottom out, but this pressure lets it be very active all the time and will help with the stiction.


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