Electrical systems, Instruments etc.

EXCHANGE ORIGINAL SPEEDOMETERS

Speedometer Calibration 

Should you wish to have your speedometer calibrated to suit your car, proceed as follows:

Ensure the rear tyres are at the correct pressure. Disconnect the speedometer cable from the instrument and attach a paper clip to the end of the inner cable. Push the car forwards a little to take up any backlash. Mark the road vertically down from the centre of the rear wheel and push the car forward 6 turns of the speedometer cable. Again mark the road directly below the centre of the same rear wheel and measure the distance between these marks in metres. Then apply the following formula, where D is the measured distance in metres, and Tm is the final number of turns required for miles per hour instrument.

D x 1.09361 = Y.
Then: 10560/Y = Tm (Turns per mile)

Should your instrument be a KPH version, convert Tm to Tk (Turns per kilometre) by multiplying Tm by 0.6213712.

Provide us with this number and your speedometer can be calibrated to this figure. The part numbers below are used for our exchange speedometer units.

If you have an MPH speedometer and would like it to be refaced and converted to read KPH (or vice versa), we can do this too at extra cost. The cost of changing the instrument mechanically is covered in the overhaul cost, the refacing of the instrument attracts an additional cost. See RTR8585 below. 

 

Axle ratio 

The Axle ratio affect's the reading of your speedometer as the drive for the speedometer is taken off the back of the gearbox (or overdrive if fitted) which is before the axle in the transmission chain.