Re: Speedometer Error?
Its an old post, but its worth pointing out that there is a tolerance involved in the production of speedos. They dont all read the same mph at the same speed. What they do, is make sure that no speedo off the production line reads slower than the actual speed.
As a result, a small proportion of speedos produced will be almost spot on. Most will read a little under. A small proportion will read much slower than actual.
You have to be wary of your satnav too. The software does all sorts of tricks behind the scenes. Look at how long it takes to recognise that you are now on a parallel road to the selected route. And notice how it displays your speed in a tunnel. Remember too, that satnavs tell you how fast you have been going, not how fast you are going. And if there are trees, buildings, bridges, lorries around, the signal can be interrupted, and the software kicks in with a best guess.
But on a straight open road, at a steady speed, they are reliable.
We have a couple of measured miles near us. I did a few runs with a pillion and stop watch maintaining steady 40, 50, 60, 70 indicated mph, just to mentally callibrate my speedo.