The reason the V8 Supercars don't is because they have a wicker on the wing that stands straight up at the top that's a couple inches. With the wing being and air brake instead of generating lift. If what you say is true then how come the old car, which had a higher rear bumper didn't pick up like this on a regular basis. Larry Mac is a former crew cheif, and Jack Roush who came up with the roof flaps, both have said it's the wing. They both have a firm understanding of areodynamics of these race cars, espacally Roush, and Indy has actually fought this problem too. Marco Andretti in the Indy 500 a few years back did this and they modified the rear wing, hasn't happened since. Also the rear of the car, with it being a quarter circle throws air up directly underneath the wing, and once the car picks up, the roof flaps deploy but the wing blocks the air going to them. The V8 Supercars are a total differant shape and are irrevlant to a Nascar Car of Today race car.
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