I have a 2013 Wrangler Unlimited Sport with the stock 16's and no lift. I'm looking at a tire/wheel package of XD Addict in 17x9 with Toyo Open Country AT in 285/70/17. From what I've researched I think these will fit, but I'd like the opinions of you all before I pull the trigger. The thing that is confusing to me is the wheel dimensions list an 18 offset, not a backspacing distance. How does one calculate backspacing from an offset dimension? Thanks!