Faux crossover gap
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. MXScandinavia provides dyno test examples of faux crossovers.
In dyno testing, faux crossovers behave like a interactive crossover. Changes to the low or high speed stack changes the damping force leading many dyno tuners to believe the crossover gap is active.
However, the crossover gap height never changes as the shim stack deflects. The crossover shims could be moved further up in the stack forming a simple tapered shim stack with the same damping force.
In dyno testing, there is no way to know the crossover gap is faux until the shock is pushed to high enough speed to observe the crossover closing. Soft closures of interactive crossovers make those events difficult to spot in damping force data.
High speed damping (mx9c)
Softening or stiffening the high speed stack changes the damping force everywhere, not just at high speed.
The example below from the MXScandinavia thread on Thumper Talk replaces the 0.2 mm shims in the stack taper with stiffer 0.25 mm shims.
The dyno test results (data points) show the shim stack is stiffer everywhere across the speed range, not just at high speed. Shim ReStackor calculations (shown by the lines) shows the same thing. High speed damping can be stiffened by tuning the crossover or softened using a preloading ring-shim (linky, fundamentals).
rmz450 faux crossover
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.
Shim factor scaling
MXScandinavia dyno tested shim factor equivalent shim stack configurations on Thumper Talk to determine the accuracy of shim factors in scaling suspension setups. By shim factor theory (linky, physics), a stack of 4x40.3 face shims should be 3.8% softer than a stack of 14x40.2 shims.
Dyno test results shows the actual difference was approximately double that at 7.7% shown by the data points in the figure below. Shim ReStackor analysis (lines in the figure below) show the same 7.7% difference in damping force.
