Originally Posted by TRZ06
I don't understand why the 18's would handle better than 19's.
The 19"s have a lower profile sidewall to keep the tire from rolling too much during hard cornering, thereby keeping more tire to the ground. The lower profile makes the car feel more stable and planted with less roll.
I don't get why a 40's series tires is even offered on the M.
Look at all the Ferraris, Porsches, Lambo's, Corvettes, they are using anything from 35 down to 25 series.
They ONLY reason I can see is weight. If you take the weight out of the equation, I would think a 35" 19" would corner better that a 40" 18"
You have to remember that the sidewall measurement is a ratio of how wide the tire is. For all the cars you mentioned they have very wide tires. Especially Lamborghinis and Corvettes. Another example is a bike tire. Most people that do not know how sidewall measurements work would think that a bike has an extremely low profile. In reality a bike has HUGE profile since the tires are almost as thick as they are wide.
Also I would think that the weight you save would work better for you with a smaller wheel. I am not sure but I believe weight that rotates can have a huge affect on the car so every pound counts significantly.