When the race starts, get out of your car and shoot at the other vehicles. Aim for tires and gas tanks. You might get one or two right off the bat. Afterwards, start running backwards across the course, taking out the vehicles as they drive by. You should have all of them destroyed easily by the time they're on their second or third lap. Once they change from red to white on your radar, there's no need to worry about 'em. Then just get in your car and drive through the race as normal. This works for all races, all vehicles.