How many times does this argument appear?

http://www.caranddriver.com/features...scandal-page-2

 

That's really interesting and the article states that the trip meter and therefore the odometer will be accurate, assuming you're running the factory tire size.

I think the reasons that the car manufacturers build in the overestimatation is ridiculous. Sell the car with an accurate speedometer... If I put bigger tires on making the actual speed higher than the displayed speed, then that's on me. Or better yet make it easily adjustable.

 

"I think the reasons that the car manufacturers build in the overestimatation is ridiculous. Sell the car with an accurate speedometer... If I put bigger tires on making the actual speed higher than the displayed speed, then that's on me. Or better yet make it easily adjustable."

The reasons the manufacturers do so is because they are regulated by ece-r 39 as cited and linked in the article. If they were to follow your rules they would only be able to sell cars in your kingdom. OTOH I nominate you for world leader for a day. More if you can stand it.

 

The European regulation, ECE-R 39

 

Here is the regulation: https://www.unece.org/fileadmin/DAM/...gs/r039r1e.pdf

You said before, "the European Union in it's infinite wisdom has mandated that speedometers show a 3 to 4 MPH difference from actual.". That is absolutely not true.

The regulation says in paragraph 5.3,
The speed displayed is allowed to be within the range of (actual speed) and (actual speed + 10% + 4 km/h).

 

It is not literally true but the effect of the regulation does force manufacturers to overstate speed in order to avoid it being understated with reasonable increases in tire diameter.

On-line query results:

The ECE is not the European Union but the EU did change their regulation to match.

The current US regulation appears to be +/- 10% (2005) and was previously +/- 5%.

 

And as your tires wear and when your tires are cold, especially in the winter, accuracy will change.