Final Drive Ratio Calculator - Calculator Academy

Reviewed By: Patrick Myers (BSME)

Enter the axle ratio, transmission gear ratio, and transfer case ratio into the calculator to determine the final drive ratio.

Final Drive Ratio Formula

The following formula is used to calculate the final drive ratio of a car.

DR = AR * TR * TCR

Where DR is the drive ratio (ratio :1)
AR is the axle ratio : 1
TR is the transmission gear ratio : 1
TCR is the transfer case ratio : 1

To calculate a final drive ratio, multiply the axle ratio by the transmission gear ratio, then multiply this result by the transfer case ratio.

Final Drive Ratio Definition

A final drive ratio is defined as the final ratio between the engine rpm to the wheel rpm of a car or vehicle.

Final Drive Ratio Example

How to calculate the final drive ratio?

First, determine the axel ratio.
For this example we will say the axel ratio is 5:1.
Next, determine the transmission ratio.
For this example the transmission ratio is 2:1.
Next, determine the transfer case ratio.
For this example and most cases this is 1:1 on the high end.
Finally, calculate the final drive ratio.
Using the equation above we find the drive ratio to be 10:1

FAQ

What is a final drive ratio?

A final drive ratio is the ratio of the RPM of an engine to the RPM delivered to the wheels of a vehicle.

Follow-Up Calculations

A 3.73:1 final drive means one wheel revolution takes 3.73 driveshaft revolutions, so if the wheels are at 800 rpm the transmission output shaft is around 2,984 rpm. The shaft-speed calculation is useful when you know road speed or wheel rpm and want to check whether the drivetrain is staying within a safe operating range.

If your final drive ratio is 3.73:1 and the transmission is in a 1:1 gear, an engine spinning 3,000 rpm sends the wheels to roughly 804 rpm before tire size turns that into road speed. The wheel RPM check helps you compare gear swaps, because a taller tire or a shorter axle ratio can change the same cruising speed by hundreds of wheel revolutions per minute.

Swapping from a 3.31:1 axle to a 3.73:1 axle changes the rotation rate by about 12.7%, so a speedometer calibrated for the old gearing can start showing the wrong miles and MPG. After a gear change, the odometer adjustment tool helps you translate indicated distance into real-world miles, which matters when you are tracking fuel economy or maintenance intervals.