31″ tires max. I have a Grand Cherokee also, with the 2″ lift, and run 31×10.5×15 BFG All Terrains. If you go any larger than that (33″, etc.), you will have less flex capabilities, the tires will rub in the wheel-wells more often, and it will make for more trouble offroad. However, with the 16″ rim size, it will be harder to find the right size tires.
Hope it helps!
