I don't expect 100% accuracy but equally I don't expect the 8-10% over I had on a previous Golf.

Would be interested to hear any feedback.

I was checking this within my daughter's new Mii.

Speedo @ 30mph = GPS @ 28mph

Speedo @ 50mph = GPS @ 47mph

Speedo @ 75mph = GPS @ 71mph

 

The average is around 6% over-read with brand new fully-inflated tyres. 

 

Depends on the tyre combo, when I had 175 it was about 4-5 mph under, with 205 tyres it's more closer to 2-3 mph under

Hyphons - you say 'under' by which I presume you meant that the speedo was showing a lower speed  ?

From the factory on OEM tyre sizes new, then when wearing a bit the Speedo will read faster than the car is going.

Fitting larger circumference tyres might have it more to the accurate speed even if comparison tables say that it will read wrongly.

http://kouki.co.uk/utilities/visual-tyre-size-calculator

 

im not sure how accurate

 

 

I pretty sure vehicle manufacturers are allowed to fit speedos that show a speed in excess of actual, up to 10% I think. A satnav GPS is the accurate one.