This will answer everything...
Tire Size Calculator - tire & wheel plus sizing

If you plug in any of the 3 factory wheel options, you'll see they're all just over 26.5". If you want to run another size like 275/40R18, you can plug different sizes into that calculator until you come up with a near 26.5" diameter.

if you like your tires stretched,,,,i run 245/45 up front & 275/40 in rear.
both are 26.7" tall & performance is great!:ughdance:

A few points worth mentioning:

1) Tires do not all weigh the same
2) Tires will affect handling just as much or more than wheels
3) I use a smaller diameter wheel/tire combo and have never had problems with the traction systems (on track or street).