Speedometer Gear Calculator

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This form allows you to calculate tooth counts for mechanical speedometer drives.

BETA RELEASE send any comments or suggestions to the email address below.

Disclaimer: This form is only to be used for estimation purposes. Exact results of combining equipment may vary from the estimates provided in this form. The data provided here is done so as-is with no warranty expressed or implied.

Note: This calculator has an incomplete list of tooth counts and revolutions per mile for all of the manufacturers and their speedometers. If you know values that are not listed in the drop down menus and want them listed, send them to grimmjeeper@gmail.com

There are two gears involved with a speedometer. The drive gear is the one that is either machined into the output shaft of the transmission or transfer case or it is a gear that is slipped over that shaft. It is also called the internal gear. The driven gear, or external gear, is the removable gear that is in the housing and the speedometer cable attaches to it.

This form calculates the tooth count of the external (driven) gear.

Speedometer Cable RPM
Internal Gear Teeth
Axle Gear Ratio
Tire Size Inch
Metric

/R

External Gear Teeth: