I have a 2002 Mustang Gt at stock height. I am looking at a set of Cobra R wheels 18x9 with 255/40/18 front and 275/40/18 rear. Or, a set of 17x9 rims with 275/40/17 all the way around. Any issues with the 18 inch route?

 

I'd go with the 18's. they just look alot better IMO. I have had 265 35's on the front and have 245/40 now. on the rear 305/35's DR and 285/35 for the street (I have a spare set rims for the track). I had some rubbing issues with the front with 265's before I got it aligned after lowering. Other than that, no issues. I got the 245's to save some cash and I wanted a more narrow tire up front. I checked out your tires sizes using a tire calculator (http://www.miata.net/garage/tirecalcold.html) and although your sizes will work just fine, I really like how the 265/35 - 285/35 combo looks. It's just a bit lower of a profile with some good meat on the sidewall for the rear.

Do you plan on lowering the car? If so, I'd look into C/C plates and the Bumpsteer kit, especially if you go with H&R's. Don't bother with the X2 ball joints.

Hope this helps.

 

At this point I do not plan on lowering the car. I do not race the car at all and only drive it on occassion. Just going after a look.

 

For what you described it doesn't matter which size. All personal preference either way your car will look better just depends how much more you want to spend. The tires for the 18" rims will of course be a little more expensive than the tires for the 17" rim. So just do which ever you would like