Shim Factors The dyno data we have looked at so far shows shim factors can be off by +/- 30%. What does a 30% error mean in terms of shim stack tuning? Like, how many face shims would you have to add to a stack to be off by 30%? For the MXScandinavia's baseline 14x40.2 shim stack you would have to add 10 face shims to increase the stiffness by 30%. That means using shim factors to scale one shim stack to another you could end up being off by 10 face shims. Missing your setup by 10 face shims just isn't much help for suspension tuning. For suspension tuning we need a better shim factor equation.