Hey guys, I was wondering how large of a tire can fit on certain rims. All of the wheels that I find I like are all usually around 8.5 inches wide. So I'm looking at something like an 18x8.5 set of rims (ignore offset) What is the largest tires that I can fit on the car. I have 245s on my car now with stock rims and I kinda wanna go larger, Something like 265 or so. Thanks

 

i think a 255 is maxing a 8.5 out. you'd need a 9 inch to clear a 265 tire

 

It varies slightly from tire model to tire model. Check the spec sheets on http://www.tirerack.com/ to find a good match.

-Max

 

A good rule-of-thumb is to go by the 90% rule.

Choose a tire section width that allows the rim width to support 90% of the tire's section width.

I'll use the SleepR1 fitment as an example.

255/40-17 tire mounted on a 9 x 17.

255 is ~10 inches in section width. Rim width is 9 inches. Do the division and you get 9-in rim/10-in tire or 90%. The closer to 90% the better. This is to ensure the rim is maximally supporting the tire sidewall for maximum cornering grip, and road feel.

In your example, 245 mm section width tire would follow the 90% rule. 8.5/9.6 = 89%

Note that rim width influences tire section width in 0.2 inch increments (as a general rule); for instance if you have a 255/40-17 tire section width at 10.2 inches measured on a spec rim width of 9 inches, mounting that same 255/40-17 on a 9.5 wide rim, will yield a 10.4-in tire section width--and a 10-in wide rim will yield a 10.8-in section width for that same 255/40-17.

The key to choosing the right tire width is to find the optimum size for the wheel rim. Too wide a tire for the rim width, and you don't maximize the available rubber-to-road contact patch. To narrow a tire, and you stretch the sidewall a bit too much, and you're not maximizing the tire width potential that a wider rim allows.

When choosing tire widths greater than 10-inches wide, don't forget to account for overall tire diameter. The FD's stock overall tire diameter is ~25 inches. For 17s, only 255/40-17 and 265/40-17 keep you close to 25 inches overall diameter. For 18s you have 255/35-, 265/35-, 285/30, and 295/30-series tires that keep you close to 25 inches in overall tire diameter. You see that 18s give a wider (pun intended) range of widths to choose from--at a higher cost, rougher ride, and the potential for bent rims LOL

 

Start looking at better quality wheels, you'll find wider ones.