Speedometer Gear Calculator

Enter your tire size

Tire diameter may vary slightly depending on the manufacturer.
If in doubt use manufactures posted diameter.

Metric Width: Profile (Aspect Ratio): Wheel Diameter:

Calculated tire diameter is: Change this to force a specific tire diameter.

Effective loaded tire diameter is:

Choose your rear axle gear ratio:

Speedometer Gear Selection

Select your transmission drive gear tooth count:

Calculated speedometer driven gear tooth count is:  teeth.

Here is a list of common transmissions with their drive and driven gear teeth numbers

Transmission Drive Gear Driven Gear
200-4R 10-13 26-31
TH350 7-10 17-25
TH400 15-21 32-45
700-R4 15-20 32-45
4L80E 15-18 34-45
Muncie 6-9 17-25
T-10 6 and 8 17-25
T-5 , T56 and Tremec 7-9 17-22