Keep in mind, 31" tires is a bit subjective. Actual 31x10.5 tires aren't 31" tall. They are pretty close in diameter to 245/75R16, but wider. Their diameter is influenced by tread type, and wheel width as well. 265/75R15(note 15" wheel in the size) is about identical to a 31x10.5r15. My 30x9.5 tires are pretty meaty, and are barely smaller in diameter to a mild 31" tire. I've just thrown a bunch of numbers up and added to confusion,lol. Are you wanting to run "31 inch tires" just because that's what you hear people run, or are you lifted and you have a set need? If you are lifted, then 245/75R16 is all you'll need, and will for all intents and purposes be the same diameter as a 31x10.5 tire, just not the width. If you want to run a tire that says 31x10.5r15 on it, then you need 4" offset 15" wheels, of only a couple of brands that will fit, plenty of lift, flattened pinch welds, etc.