Odometer and Speedometer Accuracy

The speedometer bias is intentional. I measure it to be an exactly 2 mph constant bias between 30–55 mph according to roadside speed radars and not to be a percentage bias. It can also be measured with a GPS app on your smartphone. The car computer is probably not accurate.

I did see the numbers for the intended bias in the OEM repair manual. 2 mph was about right. I don't remember the numbers exactly, but their range remains around 2 mph until very high speeds; then, it gets larger, about 4–5 mph or so at 90 mph as far as I can remember.