More sidewall causes more flex. More flex causes uncertain handling. Traction issues would be a little better (in a straight line drag racing sense) but cornering or panic situations would be worse. Even though tire technology has grown infinitly better as of age with alot of sidewall even the best tire runs the risk of folding on itself. With all this stability control and safety electronics on cars these days the bigger sidwall would be counterintuitive, especially on a car designed to go fast.