Speed

[propergomper]

Which is more exact my car speedo or the speed reading on my sat nav?

[Richo]

Its got to be the sat nav i think. Car speedos have moving parts and therefore i reckon they get out of sync easier.

[PhilLew]

A car speedo only needs to be 10% accurate by law.

Sat nav manufacturers don't have a vested interest in making you think a car is preforming better than it actually is.

I bet your sat naveis always reading a lower speed than your car speedo..... by about 10%

[THECORBYLOON]

Speedometers can be 10 per cent out but they must not show a speed lower than the true speed. They are set to show a speed higher than the true speed so the sat nav will be the more accurate.

[kempie]

GPS manufacturers generally quote 0.1 mph accuracy on flat ground, at constant speed and direction for several seconds and with a good sat lock.

Most car speedometers will give an incorrect speed reading. The law states that a speedo must not read slower than actual speed but can read fast +10%+4km/h.