So i have done a little research on how to adjust or gear ration based on tire sizes. This is based on the GXP's since we have the staggered sizes
changing from a 255/45/18 to a 255/35/18 drops tire size to 27" to 25"
(25.03) and drop the rears to a 225/40/18(25.09")

By dropping tire Diameter you will change the effective gear ratio. from 2.93 to a 3.16 for a 25" tall tire. A 24" tire would be 3.3:1. A 24" tall tire would be 3.43... This would be bad for fuel milage and be easier to spin the tires. but might help out over all

 

Wouldn't tire width need to change as well, even by a small margin, when lowering the aspect ratio? Or am I way off? Interesting thought, either way

 

255 is a base number, it would not change nor have any effect on tire height. The 45 / 35 to which was referred is the variable which would change the height, it is the ratio of the the tire width.

 

This is common for those that go to the track often. In fact, many people buy slicks a little smaller for this reason.

 

Exactally i was just trying to figure out what the effective gear ratio would be by changing the height of tires.