Okay so tires kinda confuse me so bear with me lol, I currently have worn out 265/75/16s on my 03 f350. They look too small, so I wanted to move up to 35s. Which I think is a 315/75/16. So the tire guy says my rims are "7" wide and I need a "7.5" wide rim, otherwise he says it will cause a blowout, I thought if I kept the last two numbers the same it was okay, anyways I didn't really get what he meant, I don't doubt him though, so what "size" rim would I need to buy, a 7.5 x 16" rim?? As in how are rims measured...