Speedos and sat nav

[cmr2payne]

Was looking at the tom tom today and compareing the readings to my speedo, Up to 70 its about the same over 70 the speedo might as well not be there :-).

Has anyone else noticed this.

Checked the tom tom in other cars and they seem spot on.

[2 sMoKiN bArReLs]

Speedo on my Chimaera is very optimistic (and it's ten miles further to St Albans from Mansfield! )

[spend]

Mine was +/- 2 mph upto 140mph on autobahn, which quite surprised me.. That was with new rubber on spider wheels which I thought might require the speedo tuning (early EBC speedo with the slot to adjust it). Remember there is a slight delay in the gps calculating the speed...

Dave

[cmr2payne]

In mine its + or - about 2 or 3 mmph upto about 70

On the motorway if you crusing at 80 sat nav says 70, if you cruse at between 90 and 95 sat nav says 80.

Must be why i havn't had a speeding ticket in it :-)

[spend]

Too much wheelspin you HOOLIGAN!

[cmr2payne]

who me :-)

[Cider Andy]

This subject appears frequently enough to wonder about what goes in with these speedo/transducer set-ups. I've read posts that suggest if the transducer is moved around to any degree it produces wildly different readings on the speedo. As the transducer is only creating pulses that are counted by the speedo, it would tend to suggest that the speedo is very sensitive to the size of the created spikes. Beyond that, the speedo must surely be capable of being calibrated (according to the number of pulses it receives over a given time).

For what it's worth, mine reads about 1 MPH lower than the sat nav reading at urban road speeds, and about 1 MPH above the sat nav at motorway speeds. More accurate than any other speedo reading I've compared to sat nav, bar a 2002 Mercedes 'C' Class I used to own, which was as accurate.

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Mine is about +/- 2 mph until 70 and over 70 its about +5mph out, which is more accurate than my Mondeo!

[spend]

At the risk of stirring up a hornets nest.... Later cars appear to use an ABS tooth ring, whereas the very early cars with GKN Diff have a nice big toothed wheel (not many slots to count).

Dave