Tom Tom Speed Accuracy

[PaleRider1975]

Just a quick question with regards to the TomTom's speed accuracy, basically there seems to be a difference between my speedometer and the TomTom by about 5 miles an hour. So my question is does anyone know which is likely to be more accurate??

[Ecom]

Hi,

The short answer is that most GPS units are accurate to within 0.1 MPH when travelling on flat ground at a steady speed and direction for more than a few seconds provided you have a good satellite fix.

Speedometers can be 10% adrift.

Regards

[freddysmith]

My TomTom 6 software under-reads my cars speedo by 4-5 mph as well.

[Bruin]

Speedos are made to over-read to stop you speeding

[Juggers2k]

Car speedometers have to over-estimate by up to 10%.
That way you will never think you are going slower than you actually are.

[TeamGers]

Yup, sounds about right to me, when my speedo reads 80mph the sat nav one is usually reading about 72mph.

[Juggers2k]

Plus of course don't forget that changes in tyre pressure and tyre wear will affect the circumference of your tyres, which in turn will affect the reading your speedo offers.

[lynx]

As indicated car speedometers are designed to read faster than true road speed...this is mandatory.