I'm fairly new to lifted jkus so I need some input. I bought a 2010 JKU with a 3 in lift. I'm running on 33inch tires and my speedometer reads 12 mph off when I'm on the highway. So if my speedometer reads 60mph, I'm actually going 72mph per a gps. What needs to be done to correct this?

 

Easiest thing is to purchase an AEV Procal...bout $150 most everywhere,

Or, you could drive 12mph "slower"

Kevin

 

So do you only have to use the procal once and then everything is recalibrated for good? When would I need to use it? I'm interested in this contraption.

 

You didn't mention if the gear ratio had been changed along with the lift. If so, that in combination with tire height that is not factory is the reason for the erroneous readings.

You use the Pro Cal and input tire height, gear ratio. It does the math and re-calibrates your speedometer module. You only have to do it once. If you go to 35's in the future you just input the new numbers and you are right again. The Pro Cal can only be used on one vehicle at a time so you can't borrow one from someone to use. It has other functions like air pressure monitor settings, idle setting and light options. Well worth the investment.