Speedometer versus car's speed on smartphone - which is more accurate?

When using Google Maps I noticed a 3mph discrepancy between my car speedometer and the phone sat-nav. Which should I rely on?

Asked on 28 December 2022 by Douglas Duthie

Answered by Lawrence Allan
Speedometers almost always over-read by a few mph due to many regions and countries having laws that state a speedo must not under-read even slightly, for a number of reasons. The most accurate speed your car is doing comes from GPS devices, so the speed on your phone is the correct one here.
Tags: speedometer
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