Depending on the age of your jeep and how sagged the springs are, your going to have more trouble with them rubbing the flares than anything. Also they will rub the lower control arms slightly on full lock turns, although it is mostly an anoying sound as opposed to being harmful to anything. If you wanna go with 30" tires or bigger I would strongly suggest a 2" budget boost for thirties and a 3" for 31"s. You can stay stock for rims up to 31" and you can put spacers on the bolts that limit travel for the turning radius so they won't rub the control arms. Largest tire you should go on a fully stock set up would be 235/75 r15. You might be able to run a 30" with stock susspension, but you'll be a street queen at best.