In a unique dyno test series MXScandinavia on Thumper Talk dyno tested two shim stack configurations and also obtained direct shim stack deflection measurements using a finger press.
A finger press inserts metal rods through the valve ports to directly measure the force required to produce a specific deflection. The MXScandinavia data shows the stiffness of the shim stack is nonlinear and the nonlinear behavior increases with stack lift. Nonlinear stiffness is one reason why the shim factor linear stiffness theory performs poorly in scaling shim stacks.
Shim ReStackor analysis of the tested shim configurations closely follows the nonlinear finger press stiffness data and the damping force data up to the dyno velocity limit of 120 in/sec. At 120 in/sec the shim stack edge lift was 0.02 inches, approximately one third of the finger press test range.
The finger press measured stack deflections well beyond the dyno test limit up to deflections of 0.06 inches equivalent to hitting a four inch bump at 200 mph.
The finger press data verifies Shim ReStackor shim stack stiffness calculations, verifies the nonlinear stiffness behavior of shim stacks at high deflections and gives confidence applying Shim ReStackor calculations at extreme conditions well beyond the limits of conventional dyno testing.