The short answer is no. You don’t “need” to,
but if you want the best performance, you might want to.
- Better Performance – Re-gearing has a much bigger impact than cold air intakes and exhaust modifications.
- Better Gas Mileage – There is a reason auto makers are putting 8 and 10 speed transmissions in vehicles.
- Use All Your Gears – Re-gearing allows use of both overdrive gears and more efficient use of the rest.
Recommended Gear Ratios
It is generally recommended to find the gear ratio that gets you close to stock RPM’s at 70mph and go up 1 or 2 ratios to make up for the added weight of tires and other accessories. If you have a diesel or Hemi, you can stick with just one ratio up.
- 4.56 Gears – Good for 35″ tires on 2.0L & 3.6L Wranglers
- 4.88 Gears – Good for 37″ tires on 2.0L & 3.6L Wranglers
- 5.13 Gears – Good for 39″ tires on 2.0L & 3.6L Wranglers
Keep in mind, there is only a 5% difference between 4.88’s and 5.13’s, which is little more than the differences between tire brands of a rated diameter. In addition, as tires wear, they get smaller. A well worn 37 inch tire can measure closer to 35 inches, which is a 5% difference!