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FERNBANK50
Occasional Visitor
Joined: Oct 13, 2003
Posts: 3
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 Posted: Tue Nov 04, 2003 11:31 am Post subject: TOMTOM SPEED ERROR? |
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The speed displayed by TOMTOM is 10% less than that of my speedo (1991 GolfGTI) which is more likely to be correct? TOMTOM or the speedo?
The error is constant over a wide speed range - from 20mph to 80+mph and has been checked on a straight road whle locked onto 6 or more satelites.
David |
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chapsworth
Regular Visitor
Joined: 02/09/2003 17:48:57
Posts: 75
Location: United Kingdom
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| Posted: Tue Nov 04, 2003 11:45 am Post subject: |
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Mine is not as much as 10% although there is a difference. I guess that it is the speedo that is going to be out. The police have to use calibrated speedos for speed checking - that would imply that the normal speedo is goint to be inaccurate.
Simon |
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NickE
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Joined: 09/10/2002 08:54:28
Posts: 47
Location: Biddenham, United Kingdom
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| Posted: Tue Nov 04, 2003 1:14 pm Post subject: |
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This all stems from an EU Directive (what else?) | Quote: | European regulation, ECE-R 39: the speedometer must NEVER read lower than a vehicle's true speed and can read as much as 10% plus 4 kph higher (4 kph = 2.4 mph).
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lbendlin
Pocket GPS Staff
Joined: 02/11/2002 22:41:59
Posts: 11878
Location: Massachusetts, USA
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| Posted: Tue Nov 04, 2003 4:19 pm Post subject: |
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yep, that's where it comes from. here in the US there's no such law, and the speedos show the correct speed. The GPS VTG signal is accurate to 0.1 km/h or 0.1 mph , so if you need to know your real speed rather believe the GPS than the speedo
Lutz
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Lutz
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FERNBANK50
Occasional Visitor
Joined: Oct 13, 2003
Posts: 3
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| Posted: Tue Nov 04, 2003 4:47 pm Post subject: |
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Thanks for all the info - looks like I can safely ignore the speedo reading and rely on TomTom
David |
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jaguar
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Joined: Nov 26, 2003
Posts: 14
Location: London, UK
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| Posted: Tue Dec 02, 2003 12:38 pm Post subject: |
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| FERNBANK50 wrote: | Thanks for all the info - looks like I can safely ignore the speedo reading and rely on TomTom
David |
David, you can't ignore the speedo unless you're travelling at a constant speed on the flat. GPS receivers have a delay, or lag, which makes driving by them for monitoring speed inadvisable. In addition. satellites only measure linear distance travelled, so if you are driving up or down a steep hill the reading will be wrong because you are not covering the same distance (in a linear sense) as you would at that speed on the flat.
I used my iPAQ to work out what the degree of error my speedo has (a hair under 10%) and now know with confidence that if I am 'doing' 75 on my speedo I am exactly on the national speed limit.
Jaguar |
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