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TOMTOM SPEED ERROR?

 
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FERNBANK50
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Joined: Oct 13, 2003
Posts: 3

PostPosted: Tue Nov 04, 2003 11:31 am    Post subject: TOMTOM SPEED ERROR? Reply with quote

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
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Joined: 02/09/2003 17:48:57
Posts: 75
Location: United Kingdom

PostPosted: Tue Nov 04, 2003 11:45 am    Post subject: Reply with quote

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
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Location: Biddenham, United Kingdom

PostPosted: Tue Nov 04, 2003 1:14 pm    Post subject: Reply with quote

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
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Joined: 02/11/2002 22:41:59
Posts: 11878
Location: Massachusetts, USA

PostPosted: Tue Nov 04, 2003 4:19 pm    Post subject: Reply with quote

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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FERNBANK50
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Joined: Oct 13, 2003
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PostPosted: Tue Nov 04, 2003 4:47 pm    Post subject: Reply with quote

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

PostPosted: Tue Dec 02, 2003 12:38 pm    Post subject: Reply with quote

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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