Can you get them recalibrated. was driving back from letchworth on sunday, and had tomtom on, I was just pottering along the A1, speedo saying 70mph, looked down at tomtom, was only doing 63mph, and stays 7mph out all throught the top speeds, then below 50mph its about 3-4mph out.

 

tom tom isn't as accurate as you would believe.

All the cars I have do this too. are you running the OE wheel size and tyre?

 

i think there is a 10% allowance rule, tom tom is correct im sure, its the tyres that give a false reading ie trye pressure, thread etc etc.. thats why speed camera's have a 10% allowance, so you can do 33mph on your clock and only be doing 30mph in real time,

 

my tom tom is different to the speedo in my van and in my scooby i wudnt go by the tom tom

 

The Tomtoms are using GPS, I would have thought that (at a constant speed) they would be really accurate? 10% underreading of a speedo isn't uncommon?

 

17" 205/45/17w its just one of them things then, i can live with it

 

Could it possibly be that your van and scooby have different transmission ratios?

I don't see the point of recalibrating as it is not possible to get it right owing to tyre wear.

The only benefit would be to reduce your mileage reading by up to 10%.

 

Mine has been the same from new,have been told it's quite normal and within tolerance.