Ford Speedometer Driven Gear Calculator

Enter the input values below and click compute. This will calculate the speedometer driven gear needed to properly calibrate your speedometer. Always recheck the speedometer calibration!  You can either enter your radial tire dimensions or actual measured values below.  Select which one you want used for calculations with these radio buttons:
Use Measured Diameter (best)Use Radial Designation


Measured Dimensions   Radial Dimensions
Gear Ratio :1 Radial Size: mm
Tire Diameter Inches  Profile: 
Speedo Drive Gear Teeth Rim Size: Inches
PSOM Exciter Ring Teeth Teeth 

Note: Programmable Speedometer/Odometer Modules (PSOM) are used on most 1992 through 1998 Ford trucks, Vans, and RV's only.  Ignore this entry, and the PSOM constant below, for other vehicles.


Revolutions/mile Rev/mile
Driven gear needed Teeth
PSOM constant
Radial Diameter:  Inches

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