I have a bone stock 03 GT convertible. I've been looking at tire and wheel packages. I wanted to put 18X9 fronts and 18X10 rears. the front tires would be 245/35/18 and the rears would be 275/35/18. What is this going to do to my gearing, speedometer and acceleration?

 

The OEM tires for the SN95 Stangs is 25.6" diameter, so the rears are exact and fronts are gonna be just under 1" smaller diameter. This can lead to some ABS sensor issues, so I recommend you go with a 40 series up front to match diameter of proposed rears. You can also go with a 285/30 out back, if you would like to stick with the proposed fronts.

Lemme guess... you are looking for a raked look?

Jazzer

 

Yes I am. I just want to avoid having this car be more sluggish off the line. So with the combination you suggested, they should be approximatly the same height as stock, even going up to 18's ?

 

Yes

It is best to keep all the tires the same diameter to avoid the ABS sensor issues mentioned. Sticking with 25.6" diameter, will avoid speedometer accuracy issues, but can easily be addressed via hand-held tuner, if you like. You will, in a sense, gain a bit more low-gearing if you go smaller than 25.6", but not much. If you are looking for better giddy-up.... much better idea to drop some new rear-end gears in your ride. I have a set of 3:55's and like them. I have been in cars with 4:10's and HATE them. By the time this guy was passing over the crosswalk on the opposite side of the intersection, he was hitting 3rd gear on an average slow take off! You will need that tuner for the replacement of gears as well, but a better way to improve your launch if interested in such things.

When looking at tires, see the "specs" for diameter of each particular size. The larger the wheel, the smaller the profile to retain the OEM size.

Jazzer

 

The tire sizes you suggested are a little small, sidewall and contact patch,
a set up like this might perform a little better and look a little beefier.

255/35 (25")
and
285/35 (26")
on there.