This chart below should help you some
Tire Size Chart
How to convert
if you don't have the chart. (Probablly easiest to just google to find a new one
The way you convert the with is convert the first number which is in mm to inches. The second number is a % of the width, it tells wheel tire size(this x2 + rim = total size in theory. Actual size might be a bit smaller). The final number is the rim size in inches.
I should really stop at that being I'm pretty new to this stuff but take the rest with a grain of salt. I have read a lot and I cannot validate it all.
32.1x10x17 (diameter x width x rim size) tires are what comes stock on the new sports with upgraded wheels. Its really close if not the same to the Rubicons. So you should be able to run anything smaller than that no problem. There are people who run 33" without a problem. If you disconnect your sway bars then you may need a small lift. The problem your going to get with going with bigger tires is the width potentially. If your going with something that is 11.5 to 12.5 wide your going to need either a spacer for the stock rims or 3.75 backspacing.
Most people end up getting new rims if they get new bigger tires. You can usually get tires and wheels for 15" wheels less than get just tires for 18" wheels. The downside is it is going to be a bit more squermy on the highway. You can air down more for offroading which is a +. I would make sure you check the forums and you should be able to see exactlly what you want in a picture before you pull the trigger.
As you get bigger your performance is going to go down. Most rear gear ratios off the dealership are 3.21 (as of 2012 at least). If your going bigger than a 33" your going to have way less power and need to re-gear your differential. Pretty pricey. Even with just going to a 33 heavier tire it can be an issue. If you are lucky and have 3.73 rear gear ratio, or your driving a manual, you'll be much better off with 33".
I would try to validate the above but hopefully I got you going in the right direction.