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YZ 250 rear shock nitrogen question

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Ok, just to get it out there so there is no confusion, I sometimes do stupid things.  Most recently I let the nitrogen out of my rear shock - don't ask.  I have read tons on posts looking for a simple answer to my question but the cloud of confusion still hangs low.  So here is the deal - I am in South GA with limited shops, none of which can re-fill shocks with nitrogen.  There are several tire shops that offer nitrogen but their machines only go to ~120 psi.  My 2003 YZ 250 calls for 142.  My question - should I just go with Nitrogen at 120 psi or is it better to just use air and get it to 142 psi until I can find a place that can re-fill with Nitrogen?  I mostly ride sand, fire breaks and single track.  Not a lot of jumping or air time.  Thanks for your help!

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120 nitrogen.. Often times I service a shock that has even less psi in it cause it's been so long and it does lose pressure over time.  120 will make the compression feel a tiny bit softer and the rebound a tiny bit slower.

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120 is no good.  The pressure in the bladder controls cavitation and foaming.  The lower you go the worse the shock will work.

I use a mountain bike shock pump.  Goes to several hundred psi.  I fill them to 150.  By the time the shock is due for service again it'll be down around 120.  Having pure nitrogen in the bladder is much less important than having the correct amount of pressure in the bladder.

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120 is no good.  The pressure in the bladder controls cavitation and foaming.  The lower you go the worse the shock will work.
I use a mountain bike shock pump.  Goes to several hundred psi.  I fill them to 150.  By the time the shock is due for service again it'll be down around 120.  Having pure nitrogen in the bladder is much less important than having the correct amount of pressure in the bladder.


Will the average rider ever know the difference between just regular air and nitrogen in a shock bladder?

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I sure doubt it.  Pure nitrogen is more stable with varying temperatures, so regular air will expand a little more when hot, causing some pressure variation.  Nitrogen increases in pressure when hot too, just not as much.  Shock oil also varies in thickness from cold to hot, so there will always be a difference once you get the shock heated up.

I've been running air for years.  Beats screwing around with nitrogen refills.  If you want to see how much difference the bladder pressure makes take the spring off of your shock, open up the clickers and compress it against the ground.  There is resistance but its a relatively insignificant amount.  Almost none compared to hydraulic damping.

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Ah, the age old question! Nitrogen and air expand the same from heat, there's some physics rule of gasses regarding this. But, canned nitrogen has less moisture, and moisture more affected by the heat. So, if you use a MTB shock pump, go to the least humid spot you can find.

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My YZ125 bladder filled to 140psi of air indoors (low humidity) using a 0-300psi MTB pump,

keeping track of pressure at the track I've only once noticed it climbed to 150psi on a really hot day.

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A quick update - I took my YZ into a local tire shop which had said they could get the pressure up to 140+ with their compressor.  It took a while but we finally got it to 140 psi.  Rode yesterday and all seemed fine.  Thanks for the input!  I like the idea of using a MTB shock pump and am going to pick one up soon.

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If they filled it with a tire chuck you probably didn't get near that into it.  You need a zero loss chuck.  Shock pump comes with one.

It'll work with 90 psi in it, just not as well as it should.  Increased tendency to pogo off of fast hits.  Make you crash kind of stuff.

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If the regulator was set to 140psi then you will get that with an air chuck. Thats how I fill my tubliss. For shocks I use zero loss chuck and nitrogen because I already had a nitrogen tank. Cant say its really any better than using air.

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