I have a stock 2002 GT and I will be pulling off the 17 inch wheels to go with a 17x9 and 17x10.5 setup. What will change if I decide to go with the same size but an 18 inch wheel. Car is stock height. Speedo issues etc?

 

I have 18s and look how much 1 tire costs, I would stick with 17s.
Nitto NT555R II Extreme
Competition Radial for Road Racing.
305/35ZR-18 101Y B
Reading the Tire Size
UTQG: 100AA

$314.00

 

Nothing will change enough to notice if you find a tire/wheel height combo that is close to stock. Since the sidewall on 18s are smaller in turn you can put together a set of 18s that are very close to the same size as a 17 with a slightly larger sidewall.

I have 18's and couldn't be happier. Don't let people scare you away from them. If you are a big racer I would recommend the 17s since they are going to be lighter and cheaper on tires. However if you just like the way they look and it's your show car or daily driver that you don't race much get the 18s. You can find somewhat cheaper tires...Summitomos are descent (good enough for my dd) and bfg makes some good ones that won't completely break the bank.

 

I had 17's with 275/40-17 on all four corners but when I saw a Mustang with 18x9 and 18x10 DD's I just had to have them...I now run 18x9 & 18x10 DD chrome bullits with 275/35-18 & 295/35-18 BFG KDWs and couldn't be happier...sure 18's cost a bit more but what the hell its only a few hundred a set...