I am looking for a 30-31inch on-off road tire for 18in hurricane wheel for my 4.6 RR. I've seen General and Nitto 255/55/18s (which is closer to a 29in tireI think), same as OEMs but wanted to see if anything available in asimilar tire but adding an inch or two in diameter. not looking to do any suspension mods anytime soon. A 30-31in tire should fit without any rubbing etc.., correct.

 

The Nitto Grappler is a great tire. Don't know how much tire clearance you have, but I have some friend who use these in the 285 size and swear by their off road abilitys as well as on road handling.
Mike