Final Drive Ratio Calculator

Inputs

Target engine speed (n_e)

Desired engine RPM at the selected road speed.

rpm

Road speed (v)

Vehicle speed for the ratio check.

km/h

Tire diameter (D)

Rolling tire diameter. Measured rolling diameter is better than nominal sidewall math.

Transmission ratio (G)

Selected gear ratio. Overdrive gears are less than 1.0.

Transfer ratio (T)

Transfer-case or auxiliary ratio. Use 1.0 if none.

Default result

Final drive ratio(F)

3.967

Pass

Also computed

Overall ratio2.975

Wheel speed(n_w)840.3rpm

Tire circumference2,075mm

Method notes 2 notes

Assumes direct mechanical coupling with no converter slip, clutch slip or tire growth.
Use measured tire revs per mile when speedometer calibration or cruise RPM needs to be exact.