The 2012 JKs seem particularly sensitive to tire size changes. Speed sensors at the wheels send speed data to the vehicle computer, and incorrect data can affect engine control and stability monitors. AEV offers their ProCal Module that can provide tire size (speedometer) correction to the computer. It can also recalibrate the computer for axle gearing changes and tire pressure–monitoring values, and offers high-idle settings for winching. You simply set the code switches on the unit and it plugs into the OBD-II port to download the programming changes to your computer.