Originally Posted by Martinmaxx
Since the overal diameter is bigger, the contact patch is also bigger (longitudinaly). The curvature of the taller wheel is flatter, and therefore, puts more rubber on the ground at once. That is why dragsters have not only wider but also taller wheels on the traction axle... (to maximize traction).
I believe this is the first BMW (not only M) to have taller rear wheels.
Porsche is also starting to use taller rear wheels now. Until the 996, they had almost identical diameters for front and rear wheels, but since the 997, they are using taller rears. For example the 997 has 235/40 18 up front and 265/40 18 on the rear, while the 993 had 225/40 18 and 265/35 18.
Thank you again Martinmaxx. This is something new to me, but glad that you opne up my eyes on this tires set up.
I notice NSX, G35, 350Z, IS350 all have taller diameter rear tire besides Ferrari, Lambo, etc.