I have an 07 JKU Sahara, how can I tell what gears I am running?

 

Easiest way is to call your dealership with the VIN # handy. They'll be able to give you a spec sheet of your build, you can guess based on year and trim, but that's really the only way to know for sure.

 

Jack up the front end, mark a spot with tape or chalk on the tire. Rotate the tire and count how many times the driveshaft rotates to the one full rotation of your tire. Make sense? 4.1 rotations of the driveshaft = 4.10 gear ratio. Repeat same thing for rear end. Should be the same ratio!!

 

You can also calculate gear ratio.

Go drive say 70 MPH (if you have an auto at a steady speed so the trans is in overdrive), note your RPM's, write down your wheel size.

Use this formula: (RPM x Tire Size inches) divided by (MPH x Transmission Ratio x 336) = Differential Ratio

An Auto JK's Overdrive ratio is 0.69:1, I believe. Someone can correct me if I'm wrong.
6th gear is 0.84:1 for the manual.

Plug in the numbers you wrote down.

For me, for example:
(1900 RPM x 32") = 60800
(70 MPH x 0.69 OD x 336 = 16228.8
60800 divided by 16228.8 = 3.74 Thus I must have the 3.73 gears.


It should give you a number close enough for you to figure out which one you have.

 

Cool, thanks all, I looked over the project jk and could not find anything, maybe that should be added.