I know there's probably already a forum about this but the search button isn't pulling up results. I just bought a set of 18*9 inch gt4 replica rims and was wondering the ideal tire size for them. Thanks in advance for the replies!

 

I'd do a 275/40/18 or maybe a 275/45...what wheels did your car come stock with?

 

The base 17 inch wheels, would 35 be too small of a sidewall?

 

Actually the 275/45 match up to basically the same as the base tire so the 35 would be way too short IMO.
http://kgm.tiwing.com/calcs/tiresizecalc.htm

 

Exactly what I was thinking, and the 275/40 would be close to the 255/40/19 of the Track Pack.

In this case, I'd do the 275/45s...

 

285/35/18 is near 255/40/19 and also almost the same as 275/40/19. I wouldn't put a 285 on a 9 inch wheel though.

 

If I were to go with a 255 size would the A/R stay 45?, don't really know a whole lot about tires lol

 

The 255/45 18 is just a little shorter than 235/50 18 which is the stock tire for any 2010-14 Mustang with an 18 inch tire
My 2010 with 255/45 18"