I used to own a 1996 Mustang GT. Not only did I go to a bigger tire, I also went with lower gears. I.E. 3.27 to 4.56 gears. I had the option of using a speedo gear but in Ford's, once you go above the gear for 3.73 gears, the speedo gears don't last long because the teeth get much thinner. I had purchased a product called a speedcal. What it does is if I changed gears or tire size, I flipped some dip switches, would drive about 10 miles and it would recalibrate the correct speed. Is there anything like that for Jeep's? I currently have 33" tires and I know the speedo is way off. Almost 10-15MPH depending on how fast I am going.

 

Just get a new speedo gear..
Should work just fine.

 

X2. I have 33's as well and bought a 30 tooth gear. It's right on the money for accuracy

 

Thanks guys. Gonna go that route then.

 

Which one will I need? My Jeep is a 2000 XJ. Do I need the short shaft or long shaft?

 

Short shaft

 

I checked my speed with the GPS for both sets of tires I run and do the math when I'm driving.

 

I have been using a GPS speedometer app on phone since I got this Jeep. I just want to fix so if my wife decided to drive my Jeep then she won't get a ticket. I know I will be upgrading gears in the future but I need to get this fixed soon. My speedometer being off is also the reason why I am only showing getting 13mpg.