Quote:
Originally Posted by mkoesel
No real change in contact patch length.
Standard M4 rolling diameter:
F: 255/35 R19 = 26"
R: 275/35 R19 = 26.6"
M4 GTS rolling diameter:
F: 265/35 R19 = 26.3"
R: 285/30 R20 = 26.7"
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It's a complex issue with many variables, and I don't claim to have all the answers. But many manufacturers are doing it, and BMW clearly had good results if they stuck with it. I'm guessing it is a factor in the vastly improved 'Ring time.
I'd imagine that the larger wheel diameter itself changes the length of the contact patch by adjusting where the weight rests. For example, if you rest a wheel on the ground (standing up as it would be when mounted) and then draw a line around the area where its weight rests (essentially a rectangle), you can see how the contact patch of a larger diameter wheel would be different than that of a smaller diameter one.