How to Determine Gear Ratios

Changing the vehicle's gear ratio is a relatively inexpensive way to dramatically change the performance characteristics of the vehicle. Altering the vehicle's gear ratio is an extremely popular performance upgrade because it requires no engine modification and the effects of the ratio change are immediately noticeable. Gear ratio is defined as the number of revolutions that the vehicle's drive train must make for the tires to make one complete revolution. For example, if a vehicle's gear ratio is 2:80, the drive train must turn two complete revolutions plus .8 ( or 80 percent) of another complete revolution for the vehicle's tires to make one revolution.

Things You'll Need

• Wrench

Instructions

1. Access the differential's internal components to reveal the gears. Some differentials have a cap which appears on the back of the differential. The cap is secured to the differential with a number of bolts. Removing the bolts with a wrench will free the cap from the differential. Other differentials have a center section that houses the gears. To remove the center-section differential, it is first necessary to remove the driveshaft. Remove the bolts that secure the driveshaft to the differential with a wrench, then pull the driveshaft away. Remove the wheels and the brakes, then remove the bolts which hold the axles to the differential housing. Pull the axles straight out of the differential. Remove the bolts that secure the differential to the differential housing, then pull the differential away.

2. Count the number of teeth on the ring gear within the differential. The ring gear is the larger circular gear.

3. Count the number of teeth on the pinion gear. The pinion gear is the smaller of the two gears.

4. Divide the number of teeth on the pinion gear into the number of teeth on the ring gear. For example, if the pinion gear has nine teeth and the ring gear has 37 teeth, the gear ratio is 4:11. This means that the drive train must turn four complete revolutions plus another .11 revolutions for the tires to make one revolution.