Off road or AT tires seem to be hard to find for the 18" wheels. I just went through this a couple months ago. The tire retailers websites only seem to list the sport truck tires in the 255/55-18 size. I searched Tire Rack, Discount Tire/Americas Tire, Les Schwab, etc. No AT tires for the 18" wheels. Then I went to the manufactures' websites, and voila!, there are actually lots of choices. You can get then at the retailers, but for some reason they don't list them on their websites. Weird. I ended up with the Toyo Open Country ATs. Definitely not as happy with them for road use as I was my Pirelli Scorpian STs. We'll see how they are off road.

 

I ended up with a set of Nitto Terra Grappler. I think I ordered them off of discount tire's web site. I was looking for something with more aggressive tread than the Goodyears and their road manners are great. NO whine, had to take it to the mount and balance place twice because of a shimmy at first but that was straightened out. They did well on a trip recently after a serious amount of rain so it was slightly muddy. The goodyears FAILED miserably. I think mine are the 255/55/18's or 265/55/18's I like them and once I wear the tread out on these I am switching to 16 wheels and may keep the Nitto's depending on wear and tear. Hope that helps.

Marc