Theoretically GPS but only when speed remains consistent. During acceleration the speedo will be closer. As a general rule speedos over-read by 5-10%
johnf_456,
May 13, 9:12pm
Gps and ^^
foxdonut,
May 13, 9:18pm
If the car is on optimal settings and the speedo is calibrated it will be more accurate than a GPS. If the car is ten years old and has tires other than factory then the GPS is probably a better option.
a laser is your best bet if you're looking for absolute accuracy I'd guess.
franc123,
May 13, 9:33pm
What are the comparative readings at 100 kph!
franc123,
May 13, 9:40pm
OK so its roughly10% higher then, its more of a concern if its the other way around for obvious reasons.Its on the outer limits of accuracy but still acceptable.
johnf_456,
May 13, 9:43pm
Sounds about right, most cars are out on purpose from factory to be on the side of caution for tickets.
singing1,
May 13, 10:48pm
So do you think that most people who pay RUC's could overpay 5 to 10 percent as it is based on the speedo k reading!
bigracket,
May 13, 10:53pm
HUH ! Speedo not odo.
tmenz,
May 14, 7:23am
A point that should be noted is that my GPS is only accurate when travelling on level roads. When going up or down hills the GPS is reading only the horizontal vector of the distance or in other words the average speed on a horizontal line from point A to point B. (presumably the speed caculation algorithm in the software doesn't factor in the altitude). The speedometer, however, is consistently reading the actual instantaneous speed over the road surface. Whether it is accurate or not! On a substantially level road, the average speed shown on a GPS over a reasonable distance should be very accurate - much more so than the average speedometer.
crzyhrse,
May 14, 1:45pm
GPS works on the change of your position in space, triangulated between satellites and a straight line between points. Not the 'horizontal' because that is a concept which does not apply to 3-dimensional space.
singing1,
May 14, 2:09pm
So you are saying that while the speed reading is not accurate the odometer is! How is that possible!
crzyhrse,
May 14, 2:12pm
It's very simple. They work independently of one another.
singing1,
May 14, 2:17pm
One cable.one worm drive on the transmission so how do they work independently of each other.
johnf_456,
May 14, 2:17pm
Correct and a good explanation.
crzyhrse,
May 14, 2:17pm
Calibration.
m16d,
May 14, 2:27pm
Yer on the Navara the speedo is 14k's out compared to the gps, but the odo is only one tenth out on the 5km distance check on the southern motorway at Drury.
crzyhrse,
May 14, 2:30pm
That's a lot.
m16d,
May 14, 4:41pm
Yer 100 on the gps is 114 on the speedo.
gedo1,
May 14, 6:07pm
You can check this on google.It is is requirement under European law that all vehicles that are sold in the European union must have a speedometer that reads "optimistically by around 7%.Since all vehicle manufacturers want to sell in that area they comply - they don't make cars that comply there and then do a different run for everywhere else in the world.That is why your vehicle speedometer is showing 100kph when your GPS shows (say) 94kph.The GPS is way more correct.Incidentally that's what makes it a problem for speeding motorists when they get clocked at (say) 115kph and then claim they were not speeding.The speedo in the vehicle was most likely showing around 118-120kph.Not a lot of excuses left after that!
johnf_456,
May 14, 6:09pm
Most cars are the opposite to this, manufacturer's tend to be on the side of caution. So 100 on the speedo in reality is often 95 94 whatever or below 100.
xr6turbo2,
May 14, 6:11pm
gps
gedo1,
May 14, 6:13pm
You're right John - I was typing too fast and got the speeds crossed up but as I was correcting it you made your post.Well done.Incidentally I deal with motoring offences rather a lot in my profession so I do have to know what I am advising is accurate and within the law - so I can say much of the comment and advice I have seen you give is sensible, rational and accurate.Don't be put off by the attacks by the irrational regular few!
iginoi,
May 14, 6:21pm
I use the navman because it uses satellites, so 1) it is more accurate than the speedo 100 navvie = 109 speedo k's and 2) it's what the police use as well (I edited out 'pigs')
tmenz,
May 14, 7:41pm
Yes, of course, but in the 'Navigator' environment, the 3D GPS coordinates appear to get 'mapped' onto the 2 dimensional maps.
johnf_456,
May 14, 7:42pm
Same in my old work hack, the speedo is out like yours to.
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