They will also have a steady-cam kit for the camera so reduce vibrations further.
Another option to try might be to use live-view on your camera so you don't have your eye to the viewfinder and can use your arms to absorb the bounces a bit and put your camera into burst mode so you can shoot 4 or 5 shots in quick succession, that way you are more likely to get one a) in focus and b) with the car where you want it.