dmwdave wrote:If the bump rubber rate gets too high then it has a dramatic effect on the handling of your car,if the front bottoms out the car will understeer,if the back bottoms out the car will step out sideways or spin.
Some of the old school guys (Frank Gardner for one)used the bump rubber as a early type of progressive spring rate before the more normal nowdays use of tender springs over the top of a main spring.This method did work very well but was very difficult to set up initially.
What Dave means by "bump rubber rate getting too high" is like when the shock bottoms out or when you use nolathane (commodore suspension bushes) for bump stops like I have.
Never seen a bump rubber with a rate specified on it. Only ones i've ever seen are the sponge bumps that are basically useless and only prevent the driver hearing a banging noise when the top of shock hits the strut top.
Dave, there is an effect on handling but not "dramatic" otherwise every car on the road that hits its bump stops would be "understeering, sideways or spinning". My car has been hitting the bump stops for years without any dramatic effects. The exception is a very bumpy corner.
I actually used Franks method recently to great effect. I installed Nolathane suspension bushes as shock bump stops and immediately trimmed 1 sec off my lap time. Benefit of what I have done is to reduce suspension travel under heavy load (compression) without the downside of using heavier rate spring. Excessive rear suspension travel was limited resulting in less diagonal jacking thereby keeping more load to the front inside wheel therefore more traction less wheelspin. I didnt notice any mid corner speed loss when I could feel stops in play, in actual fact I think mid corner was faster due to better traction. Proof is in the time.
Pros and cons of what I have done.
Pros - running softer springs (better traction for 95% of the time), reducing diagonal jacking (less wheelspin, better traction, increased corner exit speed).
Con - effectively no suspension travel during full compression (slight oversteer midcorner 5% of the time)
I would recommend what I have done as long as you calculate the correct length stops.
My car is a dedicated track car.
Retired the gti after 12000 track kms of fangin around.
Eastern creek 1.54.10, Wakefield 1.12.60 Bathurst 3.05