Valving Logic dyno tests of a kxf250 shim stack with an interactive crossover produces a crossover closure velocity of 25 in/sec. The PVP dyno data points show no evidence of crossover closure. However, the continuous damping force curve from Shim ReStackor calculations shows a subtle increase in slope at the crossover closure.

The Valving Logic kxf250 dyno data includes separate measurements of the main piston, compression adjuster and the total combined damping force. The recorded data for each component of the shock closely track Shim ReStackor calculations for the configuration and match the overall shock damping force.

A faux crossover gap never closes. Faux gaps are created by large crossover shim diameters, stiff low speed stacks or soft high speed stacks that do not produce enough force to close the crossover gap.

Valving Logic dyno tests of an rmz450 shock on Thumper Talk demonstrate the operation of a faux crossover.

Shim ReStackor analysis of the configuration shows the crossover gap eventually closes at a shaft velocity of 180 in/sec. However, the soft high speed stack used in the configuration produces virtually no change in damping force at the crossover closure. In that sense, the configuration demonstrates “faux” over the range tested.

Interactive crossovers use a shim diameter that is larger than the shim stack clamp. The larger crossover diameter transfers force from the face shims directly into the high speed stack forcing the high speed stack to deflect before the crossover closes. Interaction with the high speed stack softens the crossover closure event (linky sample apps).

Valving Logic on Thumper Talk demonstrated the performance of an interactive crossover. The damping force data shows no evidence of the crossover closing. However, Shim ReStackor calculations of the shim stack deflection and stack flow area make it easy to spot the crossover closure velocity at 20 in/sec.

MXSCandinavia went on in the thread to demonstrate the shim stack modifications needed to gain separate control of high and low speed damping:

• Preloading a soft shim stack increases damping force at low speed and softens damping force at high speed
• A crossover does the opposite with softer low speed and stiffer high speed
• A soft tapered shim stack matches the crossover stack at low speed and drops off at high speed

MXSCandinavia went on in the thread to demonstrate the shim stack modifications needed to gain separate control of high and low speed damping.

Tuning to get the desired damping force curve shape is simply done by hacking: adding or removing shim stack preload and crossovers to get the desired damping force curve shape and hacking around on stiffness to get the desired damping force value.

The numerical test bed of Shim ReStackor makes that simple, easy and intuitive.