Let's take the new Z06 for examplereeber said:See... that is exactly what I thought! He said the the total diameter of the Vette is one inch smaller exactly than the rear. This means they have the exact same sidewall height which keeps handling characteristics similar between front and rear. So, why couldn't I do that with a Mustang?
18 Front rim, 275/35 tire
19 Rear rim, 325/30 tire
The tire compensates for the rim size, bigger rim with small sidewall can equal a small rim with a bigger sidewall.