Speedo Calibration Calculators

Due to the numerous speedometer calibrations found on classic vehicles, from vehicle to vehicle and throughout their life, there may be a need to have yours recalibrated to read accurately when fitting one of our gearbox kits.

Alternatively we have electronic speedo options that can be set in the vehicle.

Use these calculators to determine if your speedo will need to be recalibrated, or to determine the calibration figure to be inputted in to one of our electronic speedometers. 

Simply input your tyre size and it will tell you the Turns Per Mile (TPM) or Kilometre (TPKM) of your wheel. If you then input your axle ratio, it will tell you the TPM/TPKM of the Mazda mechanical speedo drive, or the Pulses Per Mile/Kilometre (PPM/PPKM) of the electronic speedo drive if fitted.

Lastly, if you input your current speedo calibration (usually printed on the dial, 660 in the example below):

The calculator will then show the percentage error if you didn't recalibrate.

If the number is positive, then your speedo would read FAST (if you were travelling 60mph, it may show 65mph) and if the number is negative, your speedo would read SLOW.

NOTE: We have included a compensation for the actual rolling radius versus the calculated rolling radius. In testing we have found this to be around 3.25% as the weight of the vehicle reduces the radius of the tyre, so the calculated figures incorporate this difference automatically. 

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