It will be out by a number proportionate to the cosine of the angle of the slopeHow true this is in reality I don't know.

Speedo - 30mph
GPS - 33mph
Speedo - 70mph
GPS - 74mph
It will be out by a number proportionate to the cosine of the angle of the slope![]()

How do I access the speed thing? I have a TomTom 510... Anybody know how to get it up on screen? because I havent read the manual![]()
Anybody with TomTom able to answer the above?
from memory
main menu > change pref > skip 2 or 3 to "staus bar pref." > tick what you want


The 106GTi is about the same as that, im quite sure the Mondeo was about the same last time I had the tomtom in there.speedo 30 = GPS 27
speedo 70 = GPS 65
Cheers buddy, will try that in a bit
I want to see how much a speedo is affected from changing wheel sizes up from 14" hubs to 18" alloys![]()