Do you mean falling objects? You need to make a piece fall off the car. So it has to be premium, most people seem to have the best luck with the WRC cars. I'd do it in arcade mode, so you're not damaging a car permanently.
As for track, I don't know the best. One where you can consistently flip your car would probably work best. Turn mechanical damage off tho, otherwise you'll lose power before you can do enough damage.
Good luck.
