Reminded of this issue by another post about speedometers I have a couple of observations and questions about overriding speedometers in general.
The speedometers on mo cars these days seem to over-read by 3-5%. Now i understand that by law they have to be optimistic but in this modern day and age why is the average margin so great. My wife's 1983 2cv is much more accurate and ove-reads by maybe 2%. If I drive a car with a standalone GPS in the car this gives the speed and I see quite clearly the over-read of the speedometer. Yet on a car with a built in GPS it doesn't show the GPS calculated speed and therefore I don't see the over-read of the speedometer; why?
In France, I believe in line with other European countries, HGVs are limited to 90km/h. When following trucks on a level motorway and measuring mine and their speed with a standalone GPS I've noticed that their real speed is within about 1% of 90km/h, so their speedos/governors are much more accurate than on cars..
This isn't a rant, and I am maybe not being very clear in my points. I just don't get why in this day and age the average car speedometer is so inaccurate? Marketing?
Cheers
