How to Calculate Final Drive Ratio

by Will Charpentier

The final drive ratio determines how many revolutions your engine must develop for each rotation of the wheels. It depends on the drive ratio of your transmission, the number of teeth on the pinion gear in your differential and the number of teeth on the spur gear in your differential. It can be calculated with a bit of information from your owner's manual and your dealer, and some simple multiplication and division.

Call your vehicle dealer's service department. Ask how many teeth are on the the spur gear and pinion gear of your differential. If for any reason you can't reach the service department for your car, try visiting GlobalSpec.com to find the data. Note, however, that the service department is the more reliable source, and a the web site may provide inaccurate or outdated information.

Find your car's transmission drive ratio in the owner's manual. This is usually located in the section of the manual on Vehicle Specifications under the section on the transmission.

Divide the number of spur gear teeth by the number of pinion gear teeth. Multiply this result by your transmission final drive ratio.

Tip

  • check Your auto's dealer is always the best source of information on your car.

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About the Author

Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.