Renault Forums :: Independent Renault forum - View Single Post - Is GPS speed more reliable that speedo?

View Single Post
post #24 of (permalink) Old 2nd February 2008
Technical Supremo

Join Date: Feb 2007
Posts: 42,935
Nominated 16 Times in 67 Posts
Nominated TOTW/F/M Award(s): 28
Thanks: 372
Thanked 5,199 Times in 4,711 Posts
Just because you don't get caught speeding doesn't mean either your speedo or GPS system is accurate. That's a bit like saying I have smoked all my life but I haven't got cancer Yet!
During manufacture the speedo manufacturers have a tolerance of plus or minus 10% - but many are much more accurate than this. But to keep themselves within the law and stop being sued they will always tend to under-read. A speedo gives an instant real time display whereas a GPS system needs time over which to calculate distance. The downside of the GPS system is that it only measures over straight line distances - so if you were travelling along winding and/or undulating roads the distance measured and the actual distance travelled could be out by quite a bit. Additionally GPS satellites need to have there clocks updated at least once every 12 hours or so (this is done by the US military). Guess which satellites get ignored when they are busy - it definitely ain't the military ones that's for sure. In the interests of safety and my licience I'm sticking with my speedo reading
Currently in madnoel10's garage:
Honda Civic 1.4l
madnoel10 is offline  
For the best viewing experience please update your browser to Google Chrome