5. Myth: Large-diameter wheels fitted with low-profile tires improve handling.
Truth: Tall wheels with short sidewall tires are more about show than go. The original purpose of large-diameter wheels was to make room for larger brakes. Stylists and motorists liked the look of big wheels with short-sidewall tires and engineers took the opportunity to fit even bigger brakes. Also, low-profile tires tend to provide increased steering response, giving many the illusion of good handling. However, traction is determined largely by the composition of the tread rubber and, to a lesser extent, tire width. Pierre DuPasquier, former head of Michelin's race-tire program, said that if F1 lifted its current mandate of 13-inch diameter wheels, the size would grow to about 18 or 19 inches, "but certainly not 20 or above."
http://www.edmunds.com/car-reviews/t...icleid=129015&
Top Gear also did a test were going with a smaller sidewall helped to a point as soon as they started going with 35, 30 sidewalls the handling got a whole lot worse. That's why you see nice beefy tires on a M3 with 19" rims.