Originally Posted by mlhj83
If the M5 had 20" and the same PSS* tyres, it would be a bit quicker (lap time) than being on 19", but obviously still slightly slower than the M6.
In general, on a smooth surface, lower profile tyres will generate more grip in a corner due to less sidewall flex. Thus, if you compare the same tyre model with the same section width, but with different profiles, the lower profile tyre will be quicker round a track. The overall weight difference between the BMW M 18" and 19" with tyres on, or 19" and 20' with tyres on, isn't significant enough to make as much of a difference in lap times as sidewall flexing does. Straight line acceleration, however, should favour the lighter smaller diameter wheel, but cars spend more time in corners than they do on straights on most circuits.
I've tested my oem 219M 18s and 359M 19s with the same tyres with similar wear on the same track and the 19s generated a much better lap time and significantly less roll with improved steering response. Many people put track biased tyres on their 18s for practical reasons, which are obviously going to be quicker than 19s on the best road tyres.
exactly - and I would argue the 0-60 times would have favored the tire with the bigger contact patch in a car with as much torque as these. Either way, in order to compare apples to oranges in this comparo, I would have suggested they have the same size wheels and the same tires.