Some look a little dark to me and you need a longer lens. The Sigma 70-300 APO version (not the cheaper non-APO version) is well worth getting.
I would suggest using Tv mode if the cars are moving with AI Servo focussing, or Av mode if they're not, with One Shot focussing. Shutter speeds - depends on the effect you want. 1/320 is normally a safe bet for blurred wheels, but can drop a lot for panning shots.