Would a race car driver want a heavier or lighter car to race in?

You would want as little weight as possible on a race car, so that a smaller force can propel it to a higher speed than with a heavier vehicle. However, in most championships there are restrictions which don't allow you to go below a certain minimum weight. It is currently about 600kg in Formula 1. Sometimes, to make the car stable, extra weight may need to be added, but the design of a race car proves to (usually) be stable enough.