| Shim distortion
Flat disc shims produce a nonlinear load-deflection curve when the shims bend without distortion. Chart 3 shows a graph of a nonlinear curve.
The piston design affects shim stack distortion. These three pistons would apply the force evenly around the edge of the shim, allowing the shim to bend with minimal distortion.
Current piston designs have a 4-port design. These next two pistons are from a Showa 50mm and KYB 46mm shock.
Oil pushing on the four opposing corners of the shim stack will distort the shims as shown below.
The shim stack looses most of it's nonlinear load-deflection curve when the stack is distorted. It is hard to calculate the exact loss, but for the most part, we will assume that all 4-port pistons (of similar design) have a similar affect on the shims load-deflection curve.
- The amount of distortion affects the curve. (i.e. more distortion = flatter curve, less distortion = steeper curve)
A 4-port piston would distort the shims, producing a more linear load-deflection curve that might look something like the pink line shown below.
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