Does anybody have any idea on how accurate the speed reported by GPS device is?
I have a TOMTOM G0 500 and it report my speed at between 3 and 8 miles an hour under that of the Speedo in my car. I know that Speedo’s in cars are set by the manufactures to report a lower speed than you actually doing. But is this the same for the GPS devices?
I'd trust the GPS more than your speedo!!! Mines the same - GPS is showing about 3-4 mph slower than speedo. Never heard that about speedos showing slower on purpose!!
Why do you think the Govt. wants us all to have little black boxes in our cars. Not just for 'road pricing' but automatic speeding fines too.
Speedos usually show a speed higher than your actual speed. This is so that you can't use the speedo inaccuracy as an excuse for speeding. I think the speedo accuracy tolerance is something along the lines of -0/+10%, so sounds like the GPS speed is about spot on.
Absolutely right Finbar, speedometers are designed to over-read by up to around 10%. If you were caught speeding and it turned out that the speedo was under-reading you could sue them. Then they'd be in deep shitto.
This inaccuracy of speedometers is partly due to the problem people used to find with Volvos whose speedometer was accurate. Someone in a cheaper car (i.e. a Vauxhall) would be travelling at an indicated 60mph when in fact they were only doing 56. A Volvo driver also wishing to do 60 would be annoyed by going along at 56 and overtake. Then when they came to a built up area the true and indicated 30mph of the Volvo would be below the indicated 30 of the following car giving the impression that the Volvo driver was being slow on purpose to be annoying.
This has been discussed at length on "pocketgps". The upshot is that a GPS on straight, level ground will show, as close as is possible, a vehicle's true speed - certainly it will be more accurate than the car's speedo.
You are all right, GPS is more accurate as speedos are by law made to underread by around 10% thats why you can do the speed limit plus 10% plus 2mph before you can get done for speeding
Mine shows 77 when I'm going 70, so its the full 10%!
You used to be able to measure your speed acurately on the m'ways using the roadside makers which used to be 10 to the mile - not sure if they've gone metric now, though.
so gps is not good when going around corners or uphill or downhill. that just about rules out most of the fun on the limit driving i do. i have fitted slighter bigger wheels/tyres which makes the speedo more accurate. you can calculate how much % your diamter has increased and how much your speedo will change.
....... There's got to be a hundred reasons why i should listen to diesel owners, but right now, i can't think of any.
Originally posted by beach: so gps is not good when going around corners or uphill or downhill. that just about rules out most of the fun on the limit driving i do. i have fitted slighter bigger wheels/tyres which makes the speedo more accurate. you can calculate how much % your diamter has increased and how much your speedo will change.
Does that mean your car has done more miles than the odometer would suggest?
Originally posted by b308: Mine shows 77 when I'm going 70, so its the full 10%!
You used to be able to measure your speed acurately on the m'ways using the roadside makers which used to be 10 to the mile - not sure if they've gone metric now, though.
Does anyone know what the distances are between motorway markers these days? As your man says, it was real easy, at 60mph it would take a minute to pass ten of these (most of the cars I checked had very accurate speedos). Nowadays, I can't work out the distance (at least I could do it using the km/h scale if I knew what it was).
Well we're safe for now. Thank goodness we're in a bowling alley.
