Sometimes the best value for suspension is car's ride height from the ground, divided by ten. If the space between car's bottom and ground is 0.05, then a good suspension value would be 0.005. Lower value means, that the bottom of car's body won't hit the ground so easily, unlike with high values, which also make the body lean in turns more. Also, make sure you have defined the bounding shapes precisely, if you enter high values here.
Original C2 cars didn't seem to have very much ride height in the game, unlike in the car editing program, where they seemed to have sufficiently ride height. In their textfiles, the suspension value of 0.01 made the car's body to be lowered quite much.
0.003 = Race car, very small ride height.
0.008 = Normal car with normal ride height.
0.010 = Average, or little softer than average.
0.020 = Definitely not for race cars. Maybe for monster trucks...
Dampeners, that are in good condition, suppress the bumps, improving the handling. In bad condition, they make the car shake & 'wobble', or something like that. :-)
0.05 = Baaaaaad... partially difficult to handle, partially fun to watch.
0.3 = For low-riders maybe?
0.5 = Fun & steady ride compromise...
0.7 = Probably this is a good average value, you get quite steady ride.
1.0 = More steady ride.