GPS Speed vs Car Speedo

[Stratman]

Are they those figures the right way round? That's a very accurate speedo reading (nearest .2 mph) and the speedo should always read over, not under.

Whichever way round - that is indeed an incredibly accurate speedo. I over-read by about 5% (74mph at an actual 70).

Philip

My mistake The GPS and speedo readings were transposed. Still mighty accurate though!

 

[Brian WH]

My Garmin reads 2 mph less at 50 mph and about 3 less at 75-80+.

Don't forget Satellite navigation is only accurate in a straight line for speed, as it will assume on a bendy road that you are going in a straight line across the corners. So only check on a straight piece of road.

 

[silverarrow]

my factory fit in lexus is 3 mph out at 30 and 4 out at 80 mph
did you know the seat angle makes a difference in the speed ie looking down or up at the speedo maximum out is 10% only this is incase the car has uprated wheels or low profile tyres

 

[stats007]

There was an interesting story about an Audi driver complaining that his speedo was on the limit of over-reading (10%) and hence at 40kmiles he actually had only covered 36k, obviously devaluing his car. Audi weren't that bothered it seemed.