I have a Z Convertible and Lexus SC300 (5 Speed) and how I which I could interchange tires, since I just purchased a set of 17" BBS wheels for the Lexus. The proper diameter of the Lexus wheels are 25.74" and the n/a Z wheels are 24.86 for a .88" difference.
The wheels will fit both cars, but to keep the same diameter the aspect ratio of the tires are different.