How to Calculate the Final Drive Ratio for Rear Tires

Written by cinda roth
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Calculating the final drive ratio for rear tires lets you determine how to move your vehicle in the most efficient manner. You can also make adjustment, such as changing the tire size, to maximise the top speed and acceleration of a vehicle. By matching the tire size to the drive ratio, you can maximise fuel economy for a specific gear. Calculating the final drive ratio for the rear tires is a simple task that can be done in a few steps.

Skill level:
Moderately Easy

Things you need

  • Vehicle service manual

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  1. 1

    Locate the number of teeth in your vehicle's ring gear and the number of teeth in the vehicle's pinion gear in the service manual.

  2. 2

    Determine the transmission gear ratio by looking it up in your service manual for the gear you want to calculate a final drive ratio.

  3. 3

    Divide the number of teeth in the ring gear by the number of teeth in the pinion gear to determine the rear end ratio.

  4. 4

    Multiply the rear end ratio by the transmission gear ratio to obtain the drive ratio.

  5. 5

    Divide the rear tire size in inches by the drive ratio to determine the final drive ratio for rear tires.

Tips and warnings

  • Verify your calculations if your drive axle ratio calculation is above 4.10 because common drive axle ratios for performance vehicles are typically 4.10 or less. Ratios for non-performance vehicles are lower.
  • Single-gear vehicles, such as some motorcycles, use 1 as the transmission gear ratio.
  • If the vehicle has been modified, the teeth on the gears/sprockets may not match the number listed in the service manual. In this case, count the teeth on the sprocket.

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