Ask an expert

We just bought a car... after an AA check of course. It became obvious on the trip back from Hamilton to Whangarei that the speedometer is seriously not right. (otherwise everyone in Hamilton was driving at 60km in town and 115+ on the motorway, the cop I drove behind was driving very fast through 3 speed zones, and all the speed monitors were wrong). I've read articles, probably in the AA magazine that this is legal, but to be able to drive this car (which we are otherwise happy with) we need to know what speed to drive it at. A couple of monitors suggest that 55 on the speedo is actually 47km/h, (so maybe 58 is around 50) but how do we establish what 70km / 80km / 100km register as on the car? Also wondering if this affects the odometer as well.

Hi there,
Most vehicle odometers don't read true speed as established by GPS, and legally there a tolerance built into vehicle by the manufacturer (which is also why speed cameras have a tolerance). You may even find that everyone actually is pushing the boundaries of what they can get away with and not get a camera fine, so they are already exceeding the posted limit. If you know what the speed you are actually travelling when the electronic sign says 50 and 100 then you can allow for gradual changes in between. The more you drive a car, the more familiar you become with all these little nuances. The odometer effect would be legible, and all vehicles suffer in a similar way, some more than others.