The actual ADR for speedo accuracy is
The speed indicated shall not be less than the true speed of the vehicle. At the test
speeds specified in paragraph 5.2.5. above, there shall be the following relationship
between the speed displayed (V
1 ) and the true speed (V2).
0 ≤ (V1 - V2) ≤ 0.1 V2 + 4 km/h
So, in essence, the speedo of a car can show a speed of 100km/h if the car is doing 100km/h. Not sure where someone got the figure 7km/h difference.
When Wheels does a road test they show the speedo inaccuracy at 100. Mostly it seems to be in the range of 2-4 km/h optimistic
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