Speedo reading vs Klm travelled

[DeeJay]

OK- my speedo is cailbrated for larger tyres than those that are fitted. When I am doing 100klm/hr according to the GPS the speedo shows 105klm/hr.
What effect does this have on the odometer. Have I actually travelled more or less than what it shows?:huh:

[waynep]

I'd suggest therefore the speedo is not calibrated for those tyres. The GPS is very accurate, as long as you are travelling at a reasonably constant speed.

However it's pretty normal for the speedo to read a little higher than your actual speed - better to be over than under I guess.

It will make the same percentage difference in your odo readings. ( i.e. your odo will clock up 5% more km than you've actually done )

[p38arover]

One can't really say. Often the speed and the odometer are incorrect by differing amounts. I did a run a few days ago with my Hillman and found the speedo was low by 20% and the odo error was 8.5% low (tyres too small as the speedo was calibrated for crossply tyres of a size no longer available).

Generally speaking, and assuming correct tyre, pressures, etc, the odometer should be reasonably correct as it is, on older cars, gear driven from the gearbox output shaft.

I suggest setting the odo to zero and going for a run. After say, 10-20 km compare the odometer reading with the odometer in the GPS trip recorder.

[DeeJay]

I suggest setting the odo to zero and going for a run. After say, 10-20 km compare the odometer reading with the odometer in the GPS trip recorder.

Good thinking..thanks

The speedo is an aftermarket Autopro and calibrated for those larger Cooper tyres. Got to wear out the BFG"S now...
and I missed a critical word, it should have read than that are fitted