Super Panda454
Was also going to point out that you don't see many race cars if at all, with huge rims and low profile tires.
You don't see it because of the control tyre, category rules and previous testing. Its been proven that the 17's are up to two seconds quicker than the 18's at Sandown, and with semi slicks they're 2 seconds quicker again. That and, when you're at the tyre's adhesion limit, you do want some sidewall flex to tell you when you're about to fly off. Semi-slicks already have very stiff sidewalls compared to road tyres, so you really don't need to go low-profile.