Wider on the rear makes more sense on road and touring bikes IMO. For off road riding, a fatter tire in front seems to follow the same logic of installing suspension on the front of a rigid frame. I swapped my susp. fork for a rigid fork and now run a 2.5" tire fron 2.1" tire rear. I am not going to win any world cup XC races on it, but I can ride almost anywhere the FS bikes do.