Speedometer calculator for your Chevrolet

This will help you pick the right speedometer gears combination for your classic

If you are looking for help with restoring or hot rodding your chevy classic a good place to go for help is Chevy Talk
my favorite forum is 1955-1957 ( Modified / pro street / show) forum.

Also check out Trifive.com for 55-57 Chevy's.

Enter your tire size (the diameter may vary slightly depending on the manufacture if in doubt use manufactures posted diameter)

Metric width Profile Rim diameter or enter the diameter of the tire below

Enter the rear tire diameter Or use the tire selector above

Effective tire diameter The tire diameter is less with a load (effective tire diameter = rim diameter + (tire sidewall x 0.94))

Pick your rear end gear ratio


Select your transmission drive gear

Your speedometer cable driven gear should have 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 20-25 limited sizes available depending on drive gear O.D.
T-5 , T56 and Tremec 7-9 17-22


I appreciate any input, if you see any mistakes or any thing you would like to see added please let me know.

Any comments or suggestions please email me