Flat disc shims produce a nonlinear load-deflection curve when the shims bend without distortion.  Chart 3 shows a graph of a nonlinear curve.

Chart 3

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.

Picture 5

 

Current piston designs have a 4-port design.  These next two pistons are from a Showa 50mm and KYB 46mm shock.

Picture 6

 

Oil pushing on the four opposing corners of the shim stack will distort the shims as shown below.

Picture 7

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.

Chart 4

 

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