Quote:
Originally Posted by TahoeM3
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.
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No doubt. There is certainly some benefit to a larger wheel or BMW and others would not go that route.
I'm not necessarily convinced its about contact patch length when overall tire diameter stays effectively the same. For example, they could have went with a taller tire on the rear as well but they chose not to. Whatever benefit the 20" wheel itself may have on the length of the contact patch, increasing the tire diameter would have even more so. Clearance issues start to come into play, sure, but some of that can be mitigated with changes in the suspension or perhaps the fender lining.
It could be that the 20" wheel is there to decrease sidewall height which should reduce flex when cornering. If it helped shave even a second or two off of the Nurburgring time then that would be justified. As you note, they clearly targeted ring performance as part of their business case and marketing of the car.