So far Vulcan Grey and Glagola1 have made correct statements about damping, though they are talking about different effects due to rebound. Vulcan Grey is talking more about the fronts loosing traction due to too much high-speed rebound. Glagola1 is talking about instability due to rapid load decrease of the rear tires due to too little low-speed rear rebound.
To Vulcan Grey's point: If a bump is encountered while braking, the suspension will compress. If there is too much high-speed rebound, the load on the tire will actually decrease as the tires tries to drop back down after the bump because the damper is restricting how quickly the suspension & tire can extend. If the load decreases too much, the braking torque will overcome the friction between the tire and the ground causing the tire to lock up. This could trigger an ice mode event.
To Glagola1's point: Rear rebound is vital to controlling weight transfer during braking. Think of rebound as a tool that slows the weight transfer during a transition. During braking, weight is transferred from the rear to the front. Increasing rear rebound will slow the rate of weight transfer, keeping the rear tires loaded more for a longer period of time. The front grip increases at a slower rate and the rear grip decreases at a slower rate. Decreasing the rear rebound will allow weight transfer to occur more quickly, giving additional grip to the front tires in a shorter period of time. Similarly, more grip is being taken from the rears in a shorter period of time. This causes the feeling of instability if rear rebound is too low. Once the system reaches a steady state condition, the dampers are no longer in control of anything because the pitching motion is complete and the dampers are not compressing or extending.
In general, rebound damping steals grip from the opposite end of the car during a transient event. Compression damping adds grip to the end of the car that it is added to. Here's a summary of those statements:
Generalizations during a transition (pitch or roll, or some combination there of):
More front rebound = less rear grip
More rear rebound = less front grip
More front compression = more front grip
More rear compression = more rear grip
Of course, it is possible to go too far with compression and/or rebound damping. Too much compression will cause the tires to load too quickly, causing the car to skid. Too much rebound will cause the tire load to decrease too much, causing loss of traction.
2006 Lotus Elise
Last edited by jdawson; 09-15-2014 at 08:45 AM.