The 295/70s and the 285/75s that I have had on my truck were both rated for and mounted on the 7.5" wide factory wheel and like Lee said you can run wider but it's not the best case scenario for proper tire wear. I used to run 15" wide swappers on an 8.5" wide wheel but I never had more than 20 psi in them. I would not recommend doing that but something in the 11" to 12" wide range should be ok.
My next purchase will probably be an auxillary fuel tank. I can put it next to my rear bumper in the garage. 