Is GPS speed more reliable that speedo? - Page 5 - Renault Forums :: Independent Renault forum

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post #21 of 28 (permalink) Old 29th January 2008
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I have seen a few minimum speed limits imposed Lockerbie was one place after the Pan AM crash
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post #22 of 28 (permalink) Old 2nd February 2008
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Unhappy 10% Theory

Never rely on the plus 10% theory I was done for 31mph - in Worestershire.
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post #23 of 28 (permalink) Old 2nd February 2008
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Personally I don't know much about the +10% theory either but I do know my tom tom is more reliable than my speedo as I have passed many Gatso's and average speed camera's using my tom tom instead of my speedo. At 70 on the TT my speedo read 74, at 50 it read 53-4.

Never had a problem with speeding using this instead of my speedo. Now I know where the points are I have done it that much so don't even need my TT for that either now, lol.

All you have to do is like someone said in an earlier post, turn you GPS on and goto the speed limit then look at your speedo, just remember where the needle actualy is, I always stay about 1MPH lower than that just to be sure though.

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post #24 of 28 (permalink) Old 2nd February 2008
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Just because you don't get caught speeding doesn't mean either your speedo or GPS system is accurate. That's a bit like saying I have smoked all my life but I haven't got cancer Yet!
During manufacture the speedo manufacturers have a tolerance of plus or minus 10% - but many are much more accurate than this. But to keep themselves within the law and stop being sued they will always tend to under-read. A speedo gives an instant real time display whereas a GPS system needs time over which to calculate distance. The downside of the GPS system is that it only measures over straight line distances - so if you were travelling along winding and/or undulating roads the distance measured and the actual distance travelled could be out by quite a bit. Additionally GPS satellites need to have there clocks updated at least once every 12 hours or so (this is done by the US military). Guess which satellites get ignored when they are busy - it definitely ain't the military ones that's for sure. In the interests of safety and my licience I'm sticking with my speedo reading
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post #25 of 28 (permalink) Old 2nd February 2008
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Around me there are a few of those flashing signs that say "our speed is ... " and you get a smiling face if you're under the limit and a grumpy one if you are over it . Now, because you approach all these signs on a straightish road it happens that the sign is displaying exactly what the 'nav is saying. Therefore I feel my 'nav is pretty accurate over straight line distances.

Like others have said though I tend to go by the speedo - I would rather travel a few mph slower to avoid my license being vandalised by the fuzz!

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gps , reliable , speed , speedo

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