# How to Find a Gear Ratio for a Chevy Truck

by John Stevens J.D.Unlike many modern passenger cars, which are front-wheel drive, Chevrolet trucks are rear-wheel drive vehicles. To route the energy produced by the engine and the transmission to the rear tires, Chevy trucks use a drive shaft to connect the back of the transmission to a differential. Within the differential are two gears, which operate to turn the rear tires. The number of revolutions these gears make for each revolution of the rear tires is referred to as “gear ratio.” Before purchasing aftermarket gears, it is important to first determine which gear ratio the truck is currently equipped with.

#### Step 1

Drive the truck at a steady speed and write down the engine’s revolutions per minute or “RPMs” as noted by the tachometer, as well as the speed the truck is traveling, as measured by the speedometer.

#### Step 2

Measure the diameter of one of the rear tires with a tape measure.

#### Step 3

Multiply the number of RPMs found in Step 1 by the tire’s diameter. For example, if the tire’s diameter is 28 inches, and if the RPMs noted in Step 1 was 2,600, multiply 28 by 2,600 to reach a result of 72,800.

#### Step 4

Multiply the speed of the truck noted in Step 1 by 336. For example, if the number of RPMs was 2,600 when the truck was driven at 60 miles per hour, multiply 60 by 336 to reach a result of 20,160.

Divide the result found in Step 3 by the result found in Step 4 to determine the gear ratio. In this example, 72,800 divided by 20,160 equals 3.61. Thus, thus truck’s gear ratio is 3.61:1.

#### Items you will need

- Tape measure

- “Auto Math Handbook”; John Lawlor; 1991