just as an experiment, drive 40mph down the road with the window down. now make your hand flat, wiht your fingers together and stick it out the window like a plane wing. now angle your hand up and down. u should feel a little force trying to lift or push down your hand.

on our rc cars, i think the wing helps stabilize the rear end when flying down the bumpy straights at 40mph.

try it without and let us know how it worked out.