It'll depend a bit on your sidewall too. If you're running some pimp 28" wheels and low profile 31" slicks then you don't want a tire with excess width. 35" tires wrapped around a 16" wheel can handle the narrow wheel.
Also consider airing down on the trail. Don't want to lose beads regularly just because you want to mount a 14.5" wide tire on your stock 7.5" wheel.