TomTom Go GPS MPH

philpugh · Posted: Tue Apr 01, 2008 1:39 pm Post subject:

If what you say is true then you need to get the speedo calibrated.

The other explaination is that you have put non-spec tyres on (i.e. larger tyre size) which will put your speedo out and make it read lower (more distance for each rev of the output shaft).

Eg if the 'stock' tyre is 185*60 16inch and you fit a 225*60 18inch you'll end up nearly 16% out (slow) on your speedo.
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Mark_W · Posted: Tue Apr 01, 2008 2:55 pm Post subject:

Hi Phil,

Everything on the car is OE, as I said its 3 months old it came with the standard Alloys 17inch with 205/50x17 on them. I understand the mechanical side of this, because my Job was a car mechanic before an accident that’s how I got mates at the dealership. Like I said I will take the workshop Forman out with the GPS connected to show him how far the calibration is out on the cars Speedo.

Cheers,

Mark

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

Let us know what he says mate, as it cannot by law, show a speed LOWER than what you ACTUALLY driving.

tgold · Posted: Tue Apr 01, 2008 3:28 pm Post subject:

Mark_W · Posted: Thu Apr 03, 2008 2:53 pm Post subject:

Just had a chat with my ex colleague at the dealers and also had it confirmed with the manufactures, there is nothing you can do about it, there is no recalibration on the Speedo as it is done at the factory. Myself I can’t believe that, but there you go.

I will now drive looking at the GPS Speedo.

I wonder what would happen if I did get pulled and I said I was doing the correct speed looking at my car Speedo and then the car Speedo was check, interesting thought.

Thanks anyway,

Mark

Robin2 · Posted: Thu Apr 03, 2008 3:19 pm Post subject:

They can't fob you off with that. If your car speedo is reading lower than your true (ie GPS speed) the car is illegal and, if they can't recalibrate the existing speedo, they must give you a new one. The car is not legal to drive, so they need to give you a replacement vehicle while yours is being fixed
Robin
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Mark_W · Posted: Thu Apr 03, 2008 3:30 pm Post subject:

Border_Collie · Posted: Thu Apr 03, 2008 4:16 pm Post subject:

Meantime you could drive along at 30 then 40 then 50, with a friend or relative driving behind you watching their speedo to see any difference.
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rtj70 · Regular Visitor Joined: Jun 18, 2005 Posts: 144

If the C-Max instruments are like my previous Mondeo you can put into diagnostic mode and see a digital readout of speed.

I think you pressed in the trip reset button and held it whilst the car was started. Keep holding it in and the needles will shortly all move around clockwise and back to "zero". You are now in diagnostic mode.

Pressing the trip reset button a few times moves you to have the LCD display show your speed in MPH. This changes in realtime and the analogue dial moves slower. On the Mondeo I found this to be pretty close to tomtom speed but not the analogue dial indication of speed.

D4VE · Posted: Thu Apr 03, 2008 6:09 pm Post subject:

Taking into account that most police vehicles or Gatsos etc. are correctly calibrated but not all. Has anyone out there sucessfully used GPS as evidence over a speeding offence to help prove their actual speed.

Dave
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Andy_P · Posted: Thu Apr 03, 2008 6:18 pm Post subject:

D4VE · Posted: Thu Apr 03, 2008 6:46 pm Post subject:

All very true Andy, but GPS could possibly have been used to cast doubt on the equipment used and help towards an argument for bad calibration. Taking into account that any caibration certificates were either lost or out of date.

All subjective I know but just wondered if anyone had tried.

Dave
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tgold · Posted: Thu Apr 03, 2008 9:32 pm Post subject:

rtj70 · Regular Visitor Joined: Jun 18, 2005 Posts: 144

If you do not speed (or go above speed + 10% + 2mph) then you should be fine. But only if this is the indicated speed. If you drive at a GPS speed of say 70mph + 10% + 2mph on a motorway then the indicated speed will be a lot higher and you're in trouble.

And if you go faster than speed limit + 26mph you'll visit the magistrate's court, e.g. 97mph on a motorway.

D4VE · Posted: Thu Apr 03, 2008 10:04 pm Post subject:

I would just like to point out to any traffic cops that may be using or browsing these forums that my cruise control is always set at, or below the 10% rule.

Laughing Out Loud

Dave (real name witheld)
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