It might help if we knew what brand/type of tire you're getting. I just put a set of 30x9.50 Futura Enforcer MTs on my stock YJ and they fill the tire opening sitting on level ground. Haven't had a chance to play off road much yet but I believe they will rub a little at full flex.
If I had a digi-cam I'd post a pic. [img]images/graemlins/RockOn.gif[/img]