Calculating the maximum bumpstop allowed on a Corvette for Street class SCCA autocross may seem tricky , but it's actually pretty straight forward. Bumpstops are essentially acting as a spring, therefore the SCCA imposes additional restrictions when replacing bumpstops or shocks.
In a nutshell, bumpstops can be replaced or upgraded, however the “Initial point of contact” (when the suspension is compressed) must be the same as stock or shorter.
Here is an excerpt from the 2019 SCCA rule book:
13.5.D - A suspension bump stop is considered to be performing the Function of a spring. Therefore, the compressed length of the shock at the initial point of contact with the bump stop may not be increased from the standard part, although the bump stop may be shortened. Bump stops installed externally and concentric with the shaft of a shock may be drilled out to fit a larger diameter shock shaft. Bump stops may be substituted provided they meet the length requirements and are in the same location as stock.
So we need to measure the Initial Contact Point of the stock shocks and bumpstops with all the OEM hardware to compare with any aftermarket shock. I created a CAD model of my stock 2006 Corvette Z06 shocks which show how to take the measurements.
Since Corvettes have height adjustment from the factory, it seems like initial contact point measurement would depend on ride height. However, since Corvettes do not use coil springs attached to the shock, the initial contact point measurement is independent of ride height. The measurement will be the same if running at the top or bottom of the height range.
HOW TO MEASURE: Add DIM A and DIM B together. The rules allow the same value or smaller.
DIM A is from the lower side of the lower control arm mount to the top of the shock body.
DIM B is from the bottom of the bump stop to the mating surface of the chassis. All measurements should be taken nominally with no pre-load on any parts (wheel off and full droop).
Download PDF here: http://wix.to/-kBxA7U
The above pictures show the stock shock on the right and an aftermarket inverted style shock on the left. I didn't fill in the dimensions for the aftermarket shocks since they can vary depending on how they were spec'd.
Below are some actual measurements. Sorry, some pictures are in mm, just divide by 25.4 to get inches.
STOCK FRONT:
STOCK REAR:
Aftermarket (front and rear):
コメント