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Old 12-16-2014, 07:53 PM   #1
baloneyskin daddy OP
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suspension ?

Quick ? for any suspension gurus What effect, if any ,does changing the nitrogen pressure in a rear shock have on the performance of the shock? I have an Ohlins that was recently serviced that now needs the compression adj.set to full soft for acceptable performance. No revalving was done and to tell you the truth it may have been that way before because I simply adj the susp till it suits and never really counted the turns. The rebound is fine. Could a higher gas charge cause xtra harshness?
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Old 12-16-2014, 10:05 PM   #2
jonnyc21
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Thoughts...

I am not sure about yours but the last time I had one of my off road bikes suspension serviced it took some hours of riding tell it, in a sense, broke in a second time. If you haven't had a lot of time on the bike sense the change it might take a bit more time before it settles in?

Other options could be the use of a different brand of suspension fluid maybe? A non synthetic might run thick tell it warms up in comparison to a fully synthetic, or a little to much like a street bike shock I had once did make it stiff and ended up sending it back in to have it re-serviced... hope that gives you a bit more to think on.

Have never had any of mine over charged on the nitrogen pressure side so am not sure how that would affect things, I would think it would make it feel a little stiff but would also make the rebound feel fast or harsh, so hence the guess at the oil amount or type...
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Old 12-16-2014, 10:17 PM   #3
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I'd put 5 or so hours on it before coming to conclusions
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Old 12-16-2014, 11:34 PM   #4
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Originally Posted by VxZeroKnots View Post
...

No bike does everything perfectly. In fact, no bike does anything until someone gets on it to ride.
http://youtu.be/p5HQbeSVWs4?t=4m6s

Sorry, WAY OT, but I just couldn't resist... your tag line is obsolete


okay, not THAT obsolete, yet. But, it won't be long before the best riders and bested by machines that do better without the mushy bag of mostly water getting in the way.

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Old 12-17-2014, 12:03 AM   #5
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Quote:
Originally Posted by baloneyskin daddy View Post
Quick ? for any suspension gurus What effect, if any ,does changing the nitrogen pressure in a rear shock have on the performance of the shock? I have an Ohlins that was recently serviced that now needs the compression adj.set to full soft for acceptable performance. No revalving was done and to tell you the truth it may have been that way before because I simply adj the susp till it suits and never really counted the turns. The rebound is fine. Could a higher gas charge cause xtra harshness?
That's what pushes the oil back into the shock on rebound, it's only nitrogen so the shock doesn't explode/oil doesn't degrade so fast. The shock will get strange with low nitrogen, but it's mainly the oil doing the work on compression and although the gas does resist that a little it should be a minor effect. I'd guess fresh oil and possibly heavier , if it's still in range with the adjuster don't sweat it.

It could also be a lump of crap stuck in the compression circuit, in which case it's likely to change radically if you wind that adjuster out and back in .

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Old 12-17-2014, 09:32 AM   #6
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The main purspose of the nitrogen charge is to combat cavitation on the back side of the shock piston. This happens when the pressure drops below the vapor pressure of the fluid. When cavitation occurs tiny little air bubbles dissolved in the fluid come out and turn the shock oil into a aerated froth. Obviously, when the piston travels back through this froth there is a significant loss of damping force. One of the side effects of higher nitrogen pressure is more hysteresis in the damping. Hysteresis occurs from the higher internal pressure and manifests itself as a lag in response. This is possibly the harshness that you encountered. Typically, you would want the lowest amount of gas pressure you can get away with without getting cavitation.

http://www.mx-tech.com/articles/File...ancing2-04.pdf
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Old 12-17-2014, 12:35 PM   #7
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Thanks for the replys. I have a few long trips on the susp so its not a matter of settling in ,which was my 1st thought also.It's actually not to bad with all my gear onboard as the xtra weight helps compress the rear . It's when I have the opportunity to ride with the baggage off that the problem comes into play as I can't soften the rear.I can always recharge the nitrogen so I'll give lowering the pressure a shot just as an experiment and see what happens.I once had a nitrogen leak on a dirtbike shock and the shock became a pogo stick so it definitely has some effect, I'll post any info.
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Old 12-17-2014, 05:53 PM   #8
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It's not hard to adjust the pressure, if you can get to the Schrader valve with the shock on the bike, you could check/change it. Just saying
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Old 12-20-2014, 01:18 PM   #9
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Originally Posted by sieg View Post
It's not hard to adjust the pressure, if you can get to the Schrader valve with the shock on the bike, you could check/change it. Just saying
The volume of a typical shock reservoir is so small that just checking it with a regular tire gauge would result in the loss of quite a bit of pressure.
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Old 12-20-2014, 02:06 PM   #10
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Originally Posted by gots_a_sol View Post
The volume of a typical shock reservoir is so small that just checking it with a regular tire gauge would result in the loss of quite a bit of pressure.
Yes . As with anything, it takes the right tools. When I said: "It's not hard to adjust the pressure, if you can get to the Schrader valve with the shock on the bike, you could check/change it. " I was assuming by a competent person with the right tools, I thought it was a given that it ain't like checking your tires. Sorry if I lead anyone to think that.

If boloneyskin daddy wants to come by I'll check/adjust it for him.
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Old 12-21-2014, 01:41 PM   #11
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Quote:
Originally Posted by baloneyskin daddy View Post
Thanks for the replys. I have a few long trips on the susp so its not a matter of settling in ,which was my 1st thought also.It's actually not to bad with all my gear onboard as the xtra weight helps compress the rear . It's when I have the opportunity to ride with the baggage off that the problem comes into play as I can't soften the rear.I can always recharge the nitrogen so I'll give lowering the pressure a shot just as an experiment and see what happens.I once had a nitrogen leak on a dirtbike shock and the shock became a pogo stick so it definitely has some effect, I'll post any info.
What's the spring like? You may just be like me at the bottom of the range for that specific spring. Ohlins springs are pretty generic they span 40-50lbs. I think mine is 160-210 and I sure am at the bottom of that.

K1200RS and the recommended mounting of the compression dampener is under the seat. No on the fly adjustments that way. My dampener is mounted externally, I can just reach down for tuning on the road or I should say changing road conditions.
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Old 12-21-2014, 03:09 PM   #12
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The poor mans way to check/pressurize a shock is with a bicycle shock pump.

I'm sure the purists will squeal about not getting the nitrogen in there, but the atmosphere is is already 78% nitrogen.

The front fork on my old bike is pretty similar to a moto fork/shock, it has valving, oil, and air pressure behind the seal head. Different pressures are used depending on the weight of the rider and the sag level. Bigger rider more air.

Now a motorcycle suspension should be similar in many ways, but the pressure is just set, and not changed too much (I'm basing this on my Fox twin clicker) but my old CB900c had air ride and air shocks that you could just pressurize with regular compressed air, and the fork was the same, it rode like a dream really. But differing the pressure could really change the bikes handling. I think Goldwings have a newer self compressing setup based on this design.

They may have set the pressure towards the higher side of the tolerance for the pressure. The only way to know is to check it or have it checked. A friend with a shock pump, or $35 at the local bike shop would let you know for sure, if you know the spec. It'll likely be high pressure, IIRC my Fox TC is 350 lbs. I think my pump will go to 500lbs.
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Old 12-21-2014, 08:00 PM   #13
baloneyskin daddy OP
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I have access to nitrogen bottles so recharge is no problem for me but thanks for the offer.I did replace the rear spring with a stiffer one because the stocker was set to max preload and now its set about where it should be so theres adjustability either way.Before the spring I couldn't set my sag correctly.Now both sag settings are correct.I haven't tried the nitrogen charge pressure change yet,maybe this week.
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Old 12-23-2014, 10:31 PM   #14
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Originally Posted by baloneyskin daddy View Post
I did replace the rear spring with a stiffer one...
That might be why it feels stiffer. The charge is fine.
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Old Yesterday, 04:55 AM   #15
stainlesscycle
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Quote:
Originally Posted by mjydrafter View Post
The poor mans way to check/pressurize a shock is with a bicycle shock pump.

I'm sure the purists will squeal about not getting the nitrogen in there, but the atmosphere is is already 78% nitrogen.
that's what i use. and have been for years. works fine. purists be damned.
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