Is he crashing while generally driving the course, or is he crashing while going through the crossover, and being knocked off course by the competitors?
Bob used my stealth mclaren, and got so far in front of the competition, each time he went through a cross over, there was a genuine fear that he would be hit by a car half a lap behind him. It cost him a win a couple of times, before I watched to work out what happened. I babysat him for a win though.
But anyway, I would suggest finding a car that's significantly more powerful than the opposition, but not so much so that they build up a huge lead, even when falling into the cool zone.
If your Bob is just losing in general, and not for the reason I said, I don't know what to say...I guess your Bob could just be rubbish.