Need some advice on tire fitment. I found what I believe to be a pretty good deal on summer tires. Firestone Indy 500 - 255/40/18. My only concern is that the width might be too wide for my 18x8 wheels. Anyone have experience with this wheel & tire combination? Suspension is still completely stock. A deal's a deal, but I don't want to sacrifice any performance if that's a possibility.

 

According to Tire Rack, the rim width range is 8.5-10" for that tire, so you aren't too far off.

 

I had 255s on an 8.5 wheel and tire shops always told me they're a pain in the ***, at the limit of the wheel size, so you may be really pushing it. This was with a 35 sidewall on a 20", so of you're doing 18s, it may be doable.

 

I have 275s on a 9" wheel. There was no issue mounting them. I know plenty of guys that run 265's on 8.5, so I can't see how 255's on a 8 is an issue.

 

I think sidewall size is a factor. If it's a low profile tire vs a meaty sidewall, that's where the issue is.

 

the TRA (Tire and Rim Association) and ETRTO (European Tire and Rim Technical Organization) list a 255/40R18 fitting as 8.5 to 10.0 inch widths as with-in standard (what Tire Rack goes by).

If you have warranty on the tire, the manfucturer may void it if they find out or the installer may not honor the warranty (they may not install the tire on the wheel either)

Though is has been done, much like stretch folks mount tires outside of the standard mounting widths. The bulge will for sure affect the contact shape. It'll change the tire's characteristic in peformance and wear. but is it enough for you to feel, hard to say, i know i'm not sensitive enough to pick up changes like that.

 

It'll fit but it's not the most ideal fitment. If you're familiar with what the car feels like towards the limits of handling you'll probably notice the extra sidewall roll.