Sat Nav/Speedometer

Oct 24, 2010
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I have a Swift Sundance with the 2.2 Ducato base vehicle, there is a discrepancy between my Sat Nav and Speedometer of about 10%, does this mean that the in-board computer is also 10% out ie:the total mileage and fuel consumption?
 
Nov 19, 2010
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Possibly, but not necessarily. It depends whether speedo and mileometer are getting their info through the same route.
I suspect vehicle mfrs have a tendency to make the speedo read high on purpose, as it always reads higher than a SatNav (which works out your speed in real time from your actual movement on the surface of the planet). I can see why they'd do this, as even a slightly "low" reading could be a defence against a speeding charge, leaving them responsible. Don't know whether they do that with the mileage as well.
Your SatNav should also show the mileage travelled, so if you set your trip meter at the start of a programmed journey you can check if your mileometer is also reading high.
 
Mar 11, 2007
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So when you have to pay for a service at say 10,000 miles, you have only driven 9,000 miles and when a dealer quotes a P/X figure based on 50,000 miles, the vehicle has only done 45,000 miles.
 
Oct 24, 2010
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Thanks for your comments, I suppose it is only accademic, my intrest was in the fuel consumption, according to the computer I am getting around 36mpg(driving extremely carefully) so I am probably only getting 33 I think it is an ego thing, I will try the measured mile experiment anyway.
 

gjh

Jul 28, 2011
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We found that the difference between the speedo reading and our current Garmin sat nov differed from the difference between the speedo reading and ourold TomTom.
Sat Navs aren't all that accurate in judging positiion. Just deviate from a planned route (especially not leaving a motorway when the sat nav says so) and see how long it takes to start recalculating.
 

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