A recurring question in crossover tuning is determining the actual edge lift of the shim stack which sets the shock shaft velocity where crossover gaps closes.
Dyno tuners have developed a method to estimate shim stack deflection by installing a stiff backing plate behind the shim stack. When the face shims hit the backer the damping force kicks up giving a measure of the shaft velocity where the gap closes.
MXScandinavia shows an example of the dyno test technique on Thumper Talk.
The dyno data shows a shaft speed of 35 in/sec closes the 0.20 mm gap (data points). MXScandinavia also tested a 0.30 mm gap however his dyno could not produce the shaft speed needed to close the larger gap. Shim ReStackor calculations shown by the lines indicate the larger 0.30 mm gap closes at a shaft velocity around 65 in/sec with a damping force of 1200 lbf. The capability to evaluate shock absorber configurations at conditons well beyond the capability of conventional dynos is a unique capability of Shim ReStackor.
Determining deflection of the face shims and closure of crossover gaps is much easier with Shim ReStackor. The Shim ReStackor weight scaling spreadsheets include a slide bar on the shim stack deflection plot. Moving the slide bar pans the shim stack through the computed deflection range and positions the “F.stk” marker on each plot showing the value at that shim stack deflection.
Finding the crossover closure velocity simply requires dragging the slide bar around to close the gap on the shim stack plot. In this case a shaft velocity of 35 in/sec is needed which was verified by MXScandinavia dyno data.
