How Do You Determine Rear End Gear Ratio?

Lift the vehicle, mark the drive shaft, mark one rear tire, rotate the tire and count the revolutions of the drive shaft to determine a vehicle's rear end gear ratio. The procedure is simple and requires only a floor jack, jack stands and a roll of masking tape.

Jack up the rear end of the vehicle until the tires are off of the ground. Put a jack stand under each side of the rear axle, and lower the vehicle onto them.

After the vehicle is secure, crawl underneath the rear end, and locate the place where the driveshaft connects to the rear axle. Stick a 6-inch piece of masking tape along the driveshaft from where it connects to the rear axle towards the front of the vehicle. The tape should be straight and clearly visible when looking underneath the car from the outside by one of the rear wheel wells.

Place another piece of masking tape on the rear tire of the side that gives you a clear view of the tape on the driveshaft. Rotate the tire one complete revolution and count the revolutions that the drive shaft turns. The number of times the driveshaft rotates is the rear end gear ratio. For example, if it turns 3 1/4 turns then the ratio is 3.25 to 1.