When the speed reads 100kph on the GPS it reads 108kph on the Speedo. Which is correct!
meathead_timaru,
Dec 22, 1:21pm
GPS. Speedometers are calibrated to read high from the factory.
thewomble1,
Dec 22, 2:34pm
GPS read frompoint A to point B so if there is a curve in the road between the two points it will read the shortest distance which will not be the true speed Best on a straight piece of road. I think you will find car speedo reads faster.
thewomble1,
Dec 22, 2:43pm
I would think the more expensive the unit is the better chance being spot on. The more times per minute it tracks the satellites and uses the info to calculate the speedthe better. My GPS speedo tracks every .5 seconds to calculate the speed. My car speedo reads higher than the GPS speedo which is about the same as my GPS tracker.
r15,
Dec 22, 5:11pm
would you like to buy a gps from me "thewomble1",it's very expensive and therefore very good.
m16d,
Dec 22, 6:14pm
Must be a strange GPS if it takes a reading from point A to B. All mine take a reading from a number of satellites.
lookoutas,
Dec 22, 6:28pm
^^ That's nit-picking. But sort'v right.
splinter67,
Dec 22, 6:29pm
The gps will be closer than your speedo
pig-gal,
Dec 22, 6:47pm
I frequently go past police & speed cameras with my GPS showing 100 + or - 2km/h with no problem at all. The speedo on my 2wd Hiluxshows 110km/h at the same time. I know what I tend to believe.
chakendrick,
Dec 22, 8:18pm
Thank you for your answers, much appreciated. r15 I have an expensive GPS thanks, but self promotion can get you in hot water with TM.
arrithedog,
Dec 22, 8:30pm
Also depends if you are on a flat road or a hill doesn't it!
mrfxit,
Dec 22, 10:43pm
Somewhere back in the dark ages of an emerging motor industry that had started using instruments to measure the speed of a vehicle (speedo's) & gov't's that had found a way to confirm road speeds, There was an agreement between gov't's of the time & vehicle manufactures to deliberately calibrate speedos with a % of error increase rather then % decrease Eg: 103 verses 97 at "on road" 100 speed. (mph/kph)
mrfxit,
Dec 22, 10:49pm
D'OH
A to B Satellite to satellite
The only way a gps can compensate for hill's bends etc is triangulation & topography tracking combinations. I am presuming on a std domestic gps,. If the last signal was50m before a sharp bend & the next signal was 50m after that sharp bend then it would be a "line of sight" reading
meathead_timaru,
Dec 22, 10:50pm
GPS calculates several times a second. Curves do not make a measurable difference unless very low speed and it's only the accuracy of the position calculation and the position changing so little that causes that, such as tight turns. GPS doesn't measure the chord of the arc as you seem to be suggesting.
Another factor is available sky. they don't work well driving through gorges.
mrfxit,
Dec 22, 11:21pm
Same principle as the "bakers dozen"
msigg,
Dec 23, 1:06am
Both of them are not completely accurate. if you have to look that hard at the readout you must be speeding. Relax, take it easy, throw the electronics away, you will live longer.
thewomble1,
Dec 23, 5:04am
I don't sell GPS but from what I have heard that the 'cheaper' ones not as good as middle to expensive ones.
clwheat,
Dec 23, 5:06am
Same and i'm on the road all day long
monzaman,
Dec 23, 5:41am
My 7'' GPS seems completely accurate everywhere in Auckland except in one place,in the motor way tunnel it maintains same speed till I exit as that's only place it completely looses satelite signals to speak of.
thewomble1,
Dec 23, 5:58am
GPS units measures the shortest distance between 2 points not the arc.
kingfisher21,
Dec 23, 6:07am
Rubbish, do a bit more research.
woody1946,
Dec 23, 8:13am
There used to be signs spaced 5 miles apart. They were named "5 mile speedo check ", or something like that. So as 60 mph is 1 mile per minute, we would time that it took 5 minutes at 60mph to cover that distance
monzaman,
Dec 23, 8:58am
How far back are you going!You do know we in NZ are metric now,infact along the Bombay straight south bound there is a 5 kilometer speedo check with signs spaced at 1 k intervals.
meathead_timaru,
Dec 23, 11:47am
Actually, he's right, it calculates the straight line distance between two points. But those two points aren't the begining and end of the turning arc. You simply can't comfortably turn a normal motor vehicle tightly enough at any speed over about 20km/h to make the measured chord length significantly shorter than the true arc length. And under 20km/h what does it matter about accuracy!
woody1946,
Dec 24, 12:56am
Sorry, I never realised those speedo checks were still in use, as I have not seen them in my area. That is why I quoted it in mph.
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