I'm trying to figure out the fender rolling implications of a number of different wheel and tire combinations... A question that crossed my mind is:

Is the overall width of the rim/tire setup different if mounted on different width rims. An example would be 245 on 8.5" vs. 245 on 9". My logic says the rim width (atleast this close in size) shouldn't matter.

Thanks.

It actually makes a difference. I mounted the same 255/40 MX on 17x8 SSR that I had on 17x9 asa fr1 before you could see the difference rightaway.

I also have 8" wide MT drag slicks that looked superwide before I mounted them on 6.5" rims, it looked like the tire place gave me the wrong set of tires back after being mounted.

Thanks! I had a feeling it would matter.

Generally--tire section widths increase ~0.2 inches with every 0.5-inch increase in rim width. Thus if a 255/40-17 tire's section width is 10.2 inches when measured on a 9 wide rim, a 255 will measure 10.4 on a 9.5 wide rim, and 10.6 on a 10 wide rim.

Note that overall rim widths are ~1 inch wider than the bead-to-bead rim widths. Thus if your 255 tire measures 10.2 wide on a 9 wide rim, the sidewall is ~0.1 inch wider than the outer rim lip, which might or might not be enough to protect the rim lip from curb rash.

Check the rim width range that Tire Rack publishes under each tire model's "specs".

Generally you want 90% rim width coverage of the tire's section width. Thus a 255 is 10 inches unmounted, thus a 9 wide rim is ideal.

Thanks! I had a feeling it would matter.