TomTom versus Speedometer.

[twvw]

I have recently invested in a TomTom. Strangely this tells me I am going at a different speed to that indicated by my speedometer.

Any of you knowledgeable people know which is likely to be correct??. I have a clean licence so far and don't want to mess it up because I don't know what speed I'm really going!

[Sam]

Your speedometer is known to over read by a few mph.

I tend to go by the GPS speed on the TomTom. 80mph as indicated by the speedometer is around 76/77 on the TomTom - in Germany, on the Autobahn

[james_tiger_woo]

I think that manufacturers tend to overestimate your speed by up to 10% so that way they can't be blamed for getting you done for speeding.

[domestos]

Yes, mines the same - the TOM TOM tends to be around 2 mph slower than the speedo. The other thing I have noticed is that the cruise control seems to be 1 mph faster than the setting - i.e. cruise is 75mph and speedo says 76mph...

The TOM TOM is only accurate to 5 metres or so - so that could be the reason behind it, the TOM TOM is only calculate your speed from one GPS position to the next and the time it take you to travel that distance so is not an accurate reading IMHO - I would stick with the speedo

I have had several VW's over the last few months, 1.9 Passat, 2.0TDI Jetta and 2.0TDI Passat (hire cars and my own), and they have all been the same.

[bora(ing) nick]

Trust the Sat Nav :)

[Quatrelle]

I, too, would go with the satnav. Speedos are invariably set fast, and our Tomtom gives the same reading - 90kph at 93kph on the speedo - in both our Passat and Laguna.

The satnav will, however, only give an accurate reading for comparison on a flat (and preferably straight) road.

[DaveNN]

The SATNAV would be far more accurate....as a rule!
The car speedo will always overestimate..full stop.
I'd suggest a look at this forum & do a search on this subject....

Check out DaveNN....he's a bit of a satnav GOD!!:D

http://www.pocketgpsworld.com

[twvw]

Thank you gents.

Your assistance is as ever much appreciated!!

[domestos]

The SATNAV would be far more accurate....as a rule!
The car speedo will always overestimate..full stop.


In that case I would trust the speedo, especially if you are using it to monitor speed and not get caught by camera's... over estimation in the speedo means you are less likely to get caught...

[DaveNN]

In that case I would trust the speedo, especially if you are using it to monitor speed and not get caught by camera's... over estimation in the speedo means you are less likely to get caught...



Yeh...because you'll be doing less than the speed indicated.
SO, if you're pootling about at 70MPH (in a 70MPH limit), you'll be doing less than 70MPH.....but by how much??
Truth be known, I tend to use the satnav 'speedo' when on the motorway & keep below 80MPH (using the 'unwritten rule' that the motorway cops allow 78mph...posted limit + 10% + 1mph).