If it ever seems that your practice, test, Time Trial, and Qualifying goes better than your race, you might want to check your graphic options and make sure you don't have things turned up too high -- if you are experiencing lower framerates during race conditions than when you're doing Time Trials or Qualifying on your own, your race performance will suffer. 

Ultimately, you want to get the same framerate (or close to it) during a race with a full grid of cars as you get on your own in a Time Trial or test session. If not, scale back your graphics a bit or consider an upgrading your CPU or video card (or both).  Alternately, you can try scaling-back your graphics options so you get similar framerates with a full field of cars during race conditions as what you see during Time Trials or Qualifying by yourself.