rear shock air pressure - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 15 (permalink) Old 02-17-2013, 07:09 AM Thread Starter
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rear shock air pressure

im still trying to get my rear shock adjusted and have seen an air pressure valve at the other end, does that have anything to do with the adj. havent touched it but wondering if this does anything with the adjustment?

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post #2 of 15 (permalink) Old 02-17-2013, 07:36 AM
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It has nothing to do with adjustment.



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post #3 of 15 (permalink) Old 02-17-2013, 09:34 AM Thread Starter
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whats it for?

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post #4 of 15 (permalink) Old 02-17-2013, 09:37 AM
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Garage
Re filling the nitrogen gas... is no air in there at all.

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post #5 of 15 (permalink) Old 02-17-2013, 09:51 AM Thread Starter
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whats the pressure or p.s.i of the air/nitro that supposed to go in there? (im 13st)

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post #6 of 15 (permalink) Old 02-17-2013, 11:08 AM
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The nitrogen gas pressure in today's shocks serve two purposes.
1) Nitrogen is used as an inert gas.
2) Nitrogen is pressurized in the shock the same reason your cooling system is pressurized. It raises the boiling point of the fluid.

As the shock is worked, if the piston speed travels fast enough, or enough force applied, the fluid through the valving can reach a point where cavitation can occur.
When that does occur, the damping goes away.
By raising the pressure and therefore the boiling point, it prevents cavitation and loss of damping.

The same happens with forks, but due to economics, gas pressurization is not usually done.
If you look closely at the Ohlins forks used on WSBK and MotoGP, you'll notice a small cylinder piggy-backed onto the lower fork leg.
That's the nitrogen gas cylinder for the pressurized fork cartridges.

Traxxion-Dynamics also makes gas pressurized fork cartridges for bikes, including the RC51.

Nitrogen is used since it's an economically extractable atmospheric gas and is inert at lower temperatures.
At high temperatures it can chemically combine with other elements, but those temperatures are far higher than any reached by the suspension.
It is possible to substitute gases other than nitrogen, such as argon, but isn't really necessary.

Concerning pressure amount, the gas pressure in the shock should just be high enough to prevent cavitation, but not too high, since it could overly exert an air spring effect on the shock.
The typical value is around 150 PSI.

Most shocks are unbalanced in that internal pressure can exert differential forces between the sides of the piston due to the piston rod area.
This can cause the shock to extend fully if not constrained (air spring effect).

Balanced shocks, such as the through-shaft design used in F1 have internal pressure applied equally on both sides of the piston.
So the shock shouldn't try to extend regardless of internal pressure (no air spring effect).

Last edited by SubSailor; 02-18-2013 at 12:21 PM.
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post #7 of 15 (permalink) Old 02-17-2013, 02:31 PM Thread Starter
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um, ok cool cheers

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post #8 of 15 (permalink) Old 02-18-2013, 10:09 AM
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Just in case you were wondering, that was a truckload of knowledge that just smacked you in the face.




I'm always right.

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post #9 of 15 (permalink) Old 02-18-2013, 10:51 AM
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Quote:
Originally Posted by b.miller123 View Post
Just in case you were wondering, that was a truckload of knowledge that just smacked you in the face.
LMAO So true!
By Polarbears response, I'd say he's still spinning in awe. I am...

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post #10 of 15 (permalink) Old 02-18-2013, 12:24 PM
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Hey, he asked. I figure most folks are curious and want to know.

Unless one expects the classic Bill Cosby type of response...
"Dad, why is there air?"
"Easy son, to keep basketballs inflated".

And BTW, an example of a through-shaft damper design is a linear rod-type steering damper.
The rod area is the same on both sides of the piston as well as the gas pressure.
So one could hypothetically pressurize the hell out of that damper, but it would not affect it's movement. It would stay at whatever position you left it at.

But on a typical unbalanced shock, you increase the internal pressure and it will resist compression. (this is without spring attached).

Matter of fact, if you ever have your shock off and the spring removed, try to compress the shock.
That force resisting you is the nitrogen gas pressure.
A through-shaft design wouldn't have that. Only fluid resistance through the valving.

Last edited by SubSailor; 02-18-2013 at 12:32 PM.
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