Joined: Dec 31, 2003 Posts: 273 Location: Ngaruawahia, NZ
Posted: Mon 7th Jul 10:47am Post subject:
Running lower air pressure in a reservoir is questionable, the gas behind a floating piston is there for several reasons: displacement, to aid reabsorption of gas bubbles that are produced in the oil, in some shocks it aids in reducing bottom out, it is a form of assistants during the rebound stroke, and in some shocks produces the threshold for compression damping.
A recommendation for high performance while decreasing ( faster rebound/compression ) damping is to use a lighter weight oil, retain a high pressure in the reservoir, they are designed to tolerate a very high pressure ( dampers that don’t have Schrader valves often utilize around 200-300psi static, moto shocks use around 400psi static )
Advanced tuning requires reconfiguration of the shim stack on the rebound or compression side of the piston ( Fox, Marzocchi, Rock Shox ) SPV dampers like Swingers and 5th Element are limited to shim changes on the rebound side only, the latest trend on these shocks is to remove the stable platform valve altogether and replace it with a compression shim stack, for coil overs on DH bikes this appears an improvement ( more traction ) and adjusting the IFP position in the reservoir ( reduced air cavity ) can be beneficial in aiding the spring during bottom out as well.
Manitou shocks like the Metel use a full shim stack, no SP valve, the platform on these shocks are in the form of a check valve ( like less sophisticated propedal Fox shocks - Vanilla R and Van R ) the single ( external ) platform adjustment effecting an oil route on the compression stroke, ( via a stationary shimmed valve ) these shocks utilize up to 300lbs of gas pressure behind the IFP ( the pressure non adjustable and not user friendly! ) but can be hot rodded to become an active damper ( removing the check valve ) with an external compression and rebound adjust, then add the reservoir cap from a Swinger, and its now user friendly, ( or pinch the piston, shims and bolt from a Metel and install in a Swinger )
Those rear shocks with Schrader valves allow the rider to disassemble and custom tune their shocks for their requirements, reducing air pressure behind the IFP should only be considered a short term fix if at all, in my view the pressure, which is significant to the rate of movement in a floating piston, should be more than consistent to the action of the shock shaft and coil spring, too low a pressure and the IFP cant keep up, this causes all sorts of issues, and none beneficial to damper performance or longevity.
Joined: Oct 05, 2005 Posts: 1,461 Location: deep in the bush
Posted: Mon 7th Jul 9:47pm Post subject:
krankin wrote:
Running lower air pressure in a reservoir is questionable, the gas behind a floating piston is there for several reasons: displacement, to aid reabsorption of gas bubbles that are produced in the oil, in some shocks it aids in reducing bottom out, it is a form of assistants during the rebound stroke, and in some shocks produces the threshold for compression damping.
A recommendation for high performance while decreasing ( faster rebound/compression ) damping is to use a lighter weight oil, retain a high pressure in the reservoir, they are designed to tolerate a very high pressure ( dampers that don’t have Schrader valves often utilize around 200-300psi static, moto shocks use around 400psi static )
Advanced tuning requires reconfiguration of the shim stack on the rebound or compression side of the piston ( Fox, Marzocchi, Rock Shox ) SPV dampers like Swingers and 5th Element are limited to shim changes on the rebound side only, the latest trend on these shocks is to remove the stable platform valve altogether and replace it with a compression shim stack, for coil overs on DH bikes this appears an improvement ( more traction ) and adjusting the IFP position in the reservoir ( reduced air cavity ) can be beneficial in aiding the spring during bottom out as well.
Manitou shocks like the Metel use a full shim stack, no SP valve, the platform on these shocks are in the form of a check valve ( like less sophisticated propedal Fox shocks - Vanilla R and Van R ) the single ( external ) platform adjustment effecting an oil route on the compression stroke, ( via a stationary shimmed valve ) these shocks utilize up to 300lbs of gas pressure behind the IFP ( the pressure non adjustable and not user friendly! ) but can be hot rodded to become an active damper ( removing the check valve ) with an external compression and rebound adjust, then add the reservoir cap from a Swinger, and its now user friendly, ( or pinch the piston, shims and bolt from a Metel and install in a Swinger )
Those rear shocks with Schrader valves allow the rider to disassemble and custom tune their shocks for their requirements, reducing air pressure behind the IFP should only be considered a short term fix if at all, in my view the pressure, which is significant to the rate of movement in a floating piston, should be more than consistent to the action of the shock shaft and coil spring, too low a pressure and the IFP cant keep up, this causes all sorts of issues, and none beneficial to damper performance or longevity.
that's about the most useful thing i've read on vorb in the last 12 months, good stuff
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