It depends on how "slight" the difference is in tire size.
Once you start getting more than an inch or two difference you really want to start looking at re-gearing the axles, especially when you have a 4 cylinder.
The gear ratio in your axle is designed to work with your factory tire size. If you change one very much you really do need to change the other to compensate. In addition, as you go bigger, the tires get heavier and harder to turn (beyond just the diameter change) so you need to compensate a little more.
Try out my gear ratio calculator (Gear Ratio Calculator) with the factory tire size and the tire size you want to go to. You can try the available gear ratios with the new tires to get your RPMs and speeds to get close to the factory numbers. Then you have to decide whether it's worth the money to regear.
If you don't know what transmission or axle ratio you have (you probably have the NP231 transfer case if you have a Wrangler), post up what year and type of transmission you have (manual or auto) and people can tell you what you should have.
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