How to Find Out Your Gear Ratio on a Ford Mustang

by John Stevens J.D.

The Ford Mustang has been equipped with a number of different gear ratios in its long history. Calculating the gear ratio is important to determine whether the original gears have been changed. It is also important to determine whether to increase or decrease the existing ratio by changing to different sized gears. The larger the gear, meaning the larger the ratio, the better the gas mileage at high speeds because the engine runs slower. A smaller gear will increase acceleration, but gas mileage will suffer at high speeds as the engine runs faster.

Step 1

Measure the diameter of either rear tire with a measuring tape. Record the diameter in inches.

Step 2

Drive the Mustang at a steady speed and record the speed of the engine as indicated by the tachometer and the speed of the car as indicated by the speedometer. Record the car's speed in miles per hour rather than kilometers per hour.

Step 3

Multiply the speed of the engine by the tire's diameter. For example, if the speed of the engine was 2,500 rpm and the diameter of the tire is 26 inches, the result is 65,000.

Step 4

Multiply the speed of the car by 336. For example, if the Mustang was driven at a speed of 50 miles per hour, the result would be 16,800.

Step 5

Divide the result found in Step 3 by the result found in Step 4 to determine the gear ratio. Here, 65,000 divided by 16,800 equals 3.869. Thus, rounded up, the Mustang's gear ratio is 3.87:1.

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