Regear whenever you increase tire size by 2+ inches over stock. The most common trigger is going from stock 31s to 35s, which requires changing from 3.21 or 3.73 gears to 4.10 or 4.56. Without regearing, you lose 15-25% acceleration, fuel economy drops 2-4 MPG, and the transmission overheats during towing. Both axles must be regeared at the same time.

For 35-inch tires with the 3.6L automatic, 4.10 gears restore near-stock performance. 4.56 gears are the enthusiast choice, providing slightly better-than-stock acceleration and better off-road crawl capability. With the 3.6L manual, 4.56 is the preferred ratio. For 37-inch tires, 4.56 or 4.88 gears are recommended.

A locker forces both wheels to spin at exactly the same speed for maximum traction but makes on-road turning feel stiff. Selectable lockers (ARB, Eaton) engage only when activated. A limited-slip differential biases torque to the wheel with more grip while still allowing speed differences in turns, providing a good balance of traction and drivability for daily-driven Jeeps.

Parts (ring, pinion, install kit for both axles) cost $400-800. Professional installation runs $600-1,500 for both axles. Total cost is typically $1,000-2,500. This is not a DIY job for most people as it requires precision setup tools and experience. A poorly set up gear set will whine, overheat, and fail prematurely.