TomTom Go GPS MPH

Mark_W · Posted: Mon Mar 31, 2008 3:55 pm Post subject: TomTom Go GPS MPH

I still got my old trusted TomTom Go 300. Travelling back from Leeds to Devon this weekend, I notice that the GPS speed was 5 MPH faster than the Cars MPH.
The car is a 3 month old Ford C-Max, so which is correct, the cars MPH or the GPS MPH.
I look forward to the replies,

Mark

dhn · Posted: Mon Mar 31, 2008 4:01 pm Post subject: Re: TomTom Go GPS MPH

tgold · Posted: Mon Mar 31, 2008 4:21 pm Post subject: Re: TomTom Go GPS MPH

Border_Collie · Posted: Mon Mar 31, 2008 4:35 pm Post subject:

forky · Posted: Mon Mar 31, 2008 5:50 pm Post subject: Re: TomTom Go GPS MPH

tgold · Posted: Mon Mar 31, 2008 6:39 pm Post subject:

D4VE · Posted: Mon Mar 31, 2008 7:08 pm Post subject:

And how frustrating is it when everyone in front of you is going at 50 MPH through a series of SPECS and you can only travel at 45 MPH (TomTom speed) Laughing Out Loud

Dave

Border_Collie · Posted: Mon Mar 31, 2008 8:32 pm Post subject:

uffe73 · Posted: Mon Mar 31, 2008 8:48 pm Post subject:

john877 · Lifetime Member Joined: Mar 16, 2007 Posts: 468

my car speedo is about 5 mph faster than the sat nav which in a way is a good thing as it allows you a little margin of error

I am sure I have read it somewhere that the sat nav are more accurate than the speedo because it tracks you with a GPS signal

SatMonkey · Lifetime Member Joined: Nov 11, 2007 Posts: 45

shadamehr · Banned Joined: Apr 25, 2006 Posts: 507

The points are all covered in the thread linked to higher up.

But as it is a long thread, I will summarise the main relevant points in terms of what has been mentioned in this thread itself:

1) Speedometer can (and usually is) higher than the actual speed, but as stated MUST NOT be lower than true speed.

2) GPS indicated speed, is correct to around 0.5mph of actual speed (that is less than half of a single mph out - that's pretty darned accurate!)

3) The other thread talks long and hard about the effects of going up a hill, down a hill etc, rather than travellling a flat road in relation to the effect this will have on the gps' ability to correctly report speed. Some clever readers actually calculated however that as the maximum permitted gradient under law is of a certain value, then even allowing for travelling the steepest road in the country, this would have an all but negligible effect on the gps reported speed, and thus accuracy, in real terms.

4) You can therefore be safe in the knowledge that your gps reported speed should be highly reliable.

Hope that helps, but if you can wade through it, the other thread makes for interesting reading in places.

Mark_W · Posted: Tue Apr 01, 2008 10:36 am Post subject:

Thanks for the replies,
If what is being said that the speedometer can read over rather under, then technically if the car speedometer is reading at 70mph I am doing 75mph I am breaking that speed limit. The readings I gave were with the Cruise control, on the straight level road of a motorway with full sat connection via TomTom aerial.
I have got mates at the dealership, I think I will take the workshop Forman out with the TomTom connected to see what he says, I thought I read somewhere that the GPS speed was accurate, I wonder how many other new cars on the road are given the same reading as mine.

Re D4VE reply, yes your right, I couldn’t understand why everyone was over taking me on a Spec part of the motorway, I then set the cruise control to the speed showing on the TomTom.
Thanks for the replies.
Mark

Darren · Posted: Tue Apr 01, 2008 10:44 am Post subject:

Mark_W · Posted: Tue Apr 01, 2008 10:59 am Post subject:

Hi Darren,

My car speedo is reading under by 5mph on the GPS speed reading, so if I drive by the car speedo and increase the car speed to show on the car speedo 70mph, the true speed (by the GPS) will show I am doing 75mph.

Mark

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