Borrowed my mates Road Angel Sat Nav and noticed the speed on the GPS wasn't reading what my car was saying.

Just wondering how accurate GPS speed is ?

 

I thought it was meant to be spot on!

 

AFAIK - its measured by doppler shift of the GPS signal so should be very accurate....99.9%?

 

VERY accurate mate. Much more than ur speedo.

 

Its been commented on for years that speedos are inaccurate to around 10%.

Normally they're "ok" at around 50mph - but either side of that they tend to over-read.

Which is handy when you go through a GATSO and look at your speedo as you see it and your needle's sat just over 30

 

DRIVE YOUR CAR AT HALF SPEEDO
120 DRIVE 60
SEE WHAT THE GPS IS AND THEN SORT YOUR SPEEDO SO IT IS RIGHT

 

my 'Snooper' = 135mph, and on PF timing gear i was doing 133mpg.

My brothers 'Angel' = more accurate.

 

GPS is spot on, but there is a delay if accelerating. You need to be at the same speed for a few seconds and then look at it.

 

i was for 5 seconds.

but that will only work if the snooper/angel was under reading, not over reading.

 

ours measures speed to 5 decimal places

but it's on the tracker

 

Datron timing gear was 2mph faster than GPS monitor in car, my Stack speedo gave the same speed as Datron.