I had a 245/70/16 on mine at one time with no issues. I've seen some say that 255 is the widest without having some rubbing issues.. I think it all depends on how low you go, and the tire itself. Different tires have different tire bulge, etc... If your truck doesn't have a bunch of lean in the corners and not alot of axle flex, you could probably get a little wider in, but it would have to be perfectly centered.
