From: Autocross to Win (DGs Autocross Secrets) - Shock Forces
I’ve found that people tend to run way, way, WAY too much rebound force. The usual claim is that the extra rebound increases driver feel and makes the car feel more “planted”. It does - but it makes the car slower too. The suspension needs to work to work; if you lock it down with a lot of rebound you’re depending on the tire alone, like a go-kart.
Again, if you are in the Stock-class game, you may not have a choice but to run tons of shock force; you are prohibited by the rules from changing springs, and stiff shocks will act like “fake springs” in transitions. But once you graduate to classes that let you change springs, shock forces should plummet.
I fell into this particular trap myself. The shocks that I won the 2002 ProSolo SM Championship on were grossly overdamped, in both compression and (especially) rebound - but the car felt great! (aside from occasionally surprise snap-spinning me into the weeds, which was the bad habit that finally forced me into rethinking my setup). When I moved to a 65% critically damped setup, the car felt way less planted; way less tied down. It was actually a little bit scary, because it moved. At turn in, the car would make a definite movement in roll to the peak roll angle, and even though that roll angle was actually pretty small, all that moving around was a little bit disconcerting. The perceived loss of grip was also completely illusionary, as the data proved over and over again that the car not only had better peak grip, but it also didn’t get upset over bumps anymore. The day I crashed through one of the big Peru dips at full throttle and nearly full roll, and the car didn’t even notice… wow.
Once I got used to it, the car was faster, it was easier to drive, and it eliminated a ton of bad habits from both the car and myself. As a system, we got way faster, more often, more consistently. That’s a good thing!