Speedometer Accuracy.

Speedometers usually show speeds higher than the actual speed. European law ECE-R39 says speedos cannot show less than the actual speed AND they must never show more than 110 per cent of the actual speed plus 4 km/h. This means that the speedometer in a car going 100 km/h could legally show a speed as high as 114 km/h. But what rule do Hyundai engineers follow? Do they follow "Electric Speedometer Specifications J1226" set out by the [U.S.] Society of Automotive Engineers? It states that above 55 mph [or 88 km/h] the allowable range for speed is 4 per cent of the highest reading on the speedometer. This would mean that a speedometer on a Kona Electric going 100 km/h could legally show a speed as high as 108 km/h on its speedometer (which goes to 200 km/h).

Testing my own Kona's speedometer by comparing it with simultaneous speed-readings of a high-quality Garmin GPS, I find that my Kona's speedo is reporting 44 km/h at 40 actual; 62 km/h at 60 actual; and when showing 80 or higher speeds it is dead accurate! I never saw such accuracy in the string of BMWs I have owned over 3 decades. Mind you, you may not get this amazing accuracy if your car is shod with (the standard) Nexens. As soon as I could, I replaced the Nexens with Nokian WRG4 All Weather tires of the same (apparent) size inflated at the standard 36 pounds p.s.i. I have driven my car 4,000 km.

Factors that can change speedometer accuracy are tire wear, tire inflation, and even change of replacement tires of the same size. I suspect that 'new car' Nexens are slightly smaller than my Nokians. The only way to test this is for someone else to try the same experiment with a reliable GPS and Nexen tires.

 

Thanks for the report from NZ. By "standard tires" do you mean Nexen tires?