Speed indicator signs

You've written a lot about speedometers over-reading a car's true speed. I recently hired a car, an i30, and was driving through a village with a speed indicator sign and the sign indicated the exact speed that the speedo was reading (I would say there would have been no more than a few milliseconds between me seeing the sign and reading the speedo).

I guess these signs use radar to judge a car's speed and can be considered accurate. Have you heard that a Hyundai's speedo accurately records the true speed or is it not so clear-cut as that?

Asked on 22 June 2015 by JDM

Answered by Honest John
Speedos are generally more accurate at 30mph than at 70mph. But these side of the road speed indicators can be out by a few mph plus or minus. A GPS is the way to check and there are several smartphone speedo apps.
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