Why does my car's speedometer show a higher speed than the navigation system's speed reading?
Regulations in most countries dictate that a vehicle's speedometer cannot show a lower reading than the actual speed.
Because of this, manufacturers err on the side of caution and calibrate speedometers to always show a higher-than-actual speed. The difference can be as high as 10 per cent.
This is also partly to compensate for motorists who upsize their car wheels. Bigger wheels will lead to a higher actual speed than captured by the speedometer.
Hence, if you change to wheels which are several sizes larger than the standard-issue ones, you may want to send your car to have its speedometer recalibrated.