Originally Posted by Adriansideways
Then please tell me why has all M vehicles have a normal tyre and not run-flats? Run flats has a stiff sidewall ? And why do formula one tyres have such soft sidewalls?
Because, like everything, it's a compromise. BMW M probably preferred the way the non-run flats works with their suspension setup. Regardless, the debate isn't about run-flats vs non run-flats, it's about the same model tyre with the same section width but with different profiles. The same argument would also apply if M decided to use run-flats; the lower profile run-flat would generate more grip than a taller profile run-flat, all other things being equal.
F1 use tyres with taller profiles as the car has been designed to use the sidewall flex as a significant part of the suspension travel. If F1 cars used low profile tyres, the cars would effectively have insufficient suspension movement. This is completely different to the suspension design of a road car where there is a lot more suspension travel (excluding sidewall flex) than a F1 car, therefore, increasing stiffness with lower profile tyres for a road car can generate more grip on a sufficiently smooth surface, all other things being equal. Google F1 tyre design and suspension travel if you don't believe me.