Speedometer Correction

[gvsvic]

Is there any simple formula for knowing how much your speedometer is off when you go to 31" tires? I have an 01 TJ with 2.5 and 4:11 gears.

 

[Vlad]

http://www.go.jeep-xj.info/HowtoSpeedoGears.htm

 

[Bounty__Hunter]

Determine the percentage in change of tire height between the new and old tire sizes. Then add that percentage to your speedo.

I have speedometer gears if you want to correct it, or Dakota Digital makes an electronic speedometer calibrator (what I use) that runs about $70 or $80, can change calibration for any tire size or gear ratio.