Huey52

It's when the sidewall literally rolls over in a very hard turn and therefore scrubbing partially on same vs. more on the tread contact patch. A low profile performance tire typically has short and stiff sidewalls which helps preclude same. But as we know a very short and very stiff sidewall (e.g. 20" rim) doesn't provide much rebound/shock absorption in daily driving. Keep in mind that tires are an integral part of the suspension system, in addition to being the literal 'where the rubber meets the road' traction source. All design is compromise ... sometimes with a lean towards performance and sometimes more aesthetics.

J. Patterson

Technically speaking. Larger wheel sizes allow larger brake rotors and thus better performance on track. In street vehicles the larger wheels with ultra low profile tires are simply aesthetic fad. ( an easily damaged one at that.) You do not see racing cars on ultra low profile tires. Wider yes, but there is a need for some compliance in the tire sidewall. Stiff, yes but not a rubber wrapped allow drum. I have 19s on my S5 and they are as low profile as I care to go.

J. Patterson