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ddaddy Occasional Visitor
Joined: Nov 06, 2005 Posts: 20
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Posted: Tue Aug 15, 2006 5:10 pm Post subject: Tomtom Speed'o'meter |
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I have noticed that tomtom reports my speed as being 7-9MPH slower than my cars speedo says.
Which should I believe?
Taking into account that tomtom was connected to 10 sattelites at the time, and my car is a £600 7 year old escort.
But I do remember having a difference when driving a brand new car too.
Is tomtom accurate? |
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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 Aug 15, 2006 5:42 pm Post subject: |
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GPS is by several orders of magnitude more accurate than your car's speedo.
The police will not care though, they will tell you what they measured. _________________ Lutz
Report Map Errors here:
TomTom/TeleAtlas NAVTEQ |
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technik Lifetime Member
Joined: Mar 18, 2004 Posts: 789 Location: Midlands UK
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Posted: Wed Aug 16, 2006 1:37 pm Post subject: |
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My car speedo matches GPS speed exactly, so I would assume my speedometer is very accurate. I have also had my GPS and car speed confirmed by one of those flashing signs that shows your actual speed, so I know that GPS is correct. |
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imroberts Occasional Visitor
Joined: Jun 02, 2005 Posts: 16
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Posted: Mon Aug 21, 2006 11:24 am Post subject: |
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Typically your car will be designed so it reads about 10% over. i.e. when it reads 77 you are in fact only doing 70 (don't rely on this though!)
I noticed when I changed my wheels for a different profile that the speedo was closer to the GPS speed than it was before.
Either way though, the GPS will be more accurate |
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buphone Occasional Visitor
Joined: Aug 01, 2005 Posts: 36
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Posted: Sun Aug 27, 2006 11:02 pm Post subject: |
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"the true speed shall not exceed the indicated speed"
the error can be
http://www.opsi.gov.uk/si/si2004/20040623.htm
"the difference between the indicated speed and the true speed shall not exceed
V/10 + 6.25 mph
where V = the true speed of the vehicle in mph"
The speedo has to be designed to cope with different tyre diameter options. The GPS unit does not. |
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