Cal Club Autocross Forums

Stock Class

13.5 SHOCK ABSORBERS
A.2. Suspension geometry and alignment capability, not including
ride height, may not be altered by the substitution of alternate
shock absorbers. This includes the position of the steering
arm attachment point in the case of struts with integrated
steering arms.
A.3. Adjustable spring perches are allowed, but the spring loadbearing
surface must be in the same location relative to the
shock mounting points as on the standard part. Shims may
be used to achieve compliance.

So, 13.5.A.2 states that ride height may be change as it is not included in the restriction.

But, 13.5.A.3 states that adjustable spring perches are allowed, but the the spring load bearing surface must be the same height relative to where the shock mounts, ie so that the car remains the stock height and is not lowered.

So, I assume that adjustable spring perches are allowed just so that a slew of aftermarket shocks aren't excluded, provided the competitor adjust the perch to the stock height.

correct

exactly

I'm guessing also the rules are written as they are to avoid ride height issues brought about by gas pressures or dynamic rebound clamping.