Speedos reading over
actual speed is a design rules thing.
In most countries speedos are allowed to have an error of 10% bit must not read under
the stated speed.
Most manufacturers err on the side of caution and have to them read slightly over
Also saves on any litigation issues ("but my speedo said I was doing 55 officer"!!).
Both my Audi's are a damn site more accurate than any of my GMH products in the past - 1-2% under vs 8% under - no wonder I'm always overtaking Falcons and Commodores on the freeway...
Excerpt from Australian Design Rules:
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 (V1 ) and the true speed (V2).
0 =< (V1 - V2) =< 0.1 V2 + 4 km/h
That's actually 10% + 4km/h, which is even further out (14% at 100km/h)
edit: bold = corrections of tense