Speedometer vs. AVG MPH computer calculation

[SamirD]

Whew! I don't have to worry as much every time I'm going 15 over.

[~tc~]

Practically all cars read 2-5% faster than actual.

[ipaqxman]

Findings are consistent with mine. At higher speed the meter reads slightly higher than GPS readout.

GPS readout is consistent with meters on my recent rental cars including nissan maxima.

[SamirD]

Practically all cars read 2-5% faster than actual.

I found my Porsche actually reads more accurately as speed increases to a point. It's actually less accurate at <45.