You can put them on a 15x8, Kinda works like a poor mans bead lock and puffs the tire like a doughnut. Recommended sizes would be to shoot for a 15x10 or 12.

I've got a friend running 35/ 15.5/ 15x8 on his Cherokee at 15lbs in them. If I can find a decent pic of it I'll post it up. He runs in rocks, mud, everything he can find. Hasn't blown a bead yet. Actually he went with us Sun. and I saw it against a rock and knew it was going to loose the bead and it never did...(NOT saying it wouldn't happen).

Edit : Found the pics...