Incorrect Speedometer - Golf mkVII?

[greg32]

I was able to correct a significant amount out with VDSC in the instrument settings. The range was 1 to 7 and with the setting on 7, mine is about 2% optimistic. I haven't adjusted my wifes car yet, maybe I should make it much more optimistic by setting it to 1

[Mountainman]

According to my Garmin my speedo shows 5km/h too much at 80,100,120 - so it doesn't stick to a % increase. It also indicates 100km after only doing a real 99km. All better than my Forester which is a consistent 7% out in the speedo but only 1.3% out on the odo.

[a239947]

Thats digital speedometers for you. They can program how much of an offset they want at different speeds to maintain consistency!

this message thrown at you from the window of my flying Golf!

[pologti18t]

Thats digital speedometers for you. They can program how much of an offset they want at different speeds to maintain consistency!

Aren't all speedos nowadays electronic? They can make the needle say what ever they want

[a239947]

Pretty much, not too many running a cable anymore!

this message thrown at you from the window of my flying Golf!

[hoi polloi]

Aren't all speedos nowadays electronic? They can make the needle say what ever they want

Indeed they can.. At the end of it all they're just counting voltage pulses of one form or another - one pulse for a given unit of distance (or more accurately, angle of wheel rotation) the rate of pulses per unit of time giving speed..

Back to the ADR though, there is nothing that says the speedo *has* to be electronic - hence probably the very wide tolerance allowed not withstanding the fact the speedo can't under read... The ADR even specifies a temperature for testing (23ºC IIRC) which would affect mechanical speedos (with drag cups, hair springs etc.) more than electronic ones.. Practically every car that has an engine management computer needs a digital speed input from somewhere so it makes sense that speedos be digital too..

Personally, the only car I ever came across that was fuel injected with a mechanical speedo was the 3.0L VL Commodore (the one with the Nissan engine)... I'm sure there are others but when you consider the 5.0L V8 at the time was still carby fed you can kinda see why...

- Anthony

[CT69]

According to my Garmin my speedo shows 5km/h too much at 80,100,120 - so it doesn't stick to a % increase. It also indicates 100km after only doing a real 99km. All better than my Forester which is a consistent 7% out in the speedo but only 1.3% out on the odo.

Using GPS, my speedo overreads a consistent 5km/hr at all speeds, which is OK.
I was surprised to see the ODO under read, albeit by a tiny amount (Golf trip said 99.0km, GPS said 99.75km, less than 1% error)

[martinnw]

I had a similar issue with my Mk6 103 TDI. I checked the indicated speed against a Tom Tom GPS.
With the Mk6 I set the cruise to 125klm/h for 110 klm/hr speed limit & drove through the speed traps no problems over 3 years off hwy driving.
With the Mk7 103 TSI its a bit less & the difference is greater at higher speeds.
Cruise set to 67 for 60, 88 for 80, 110 for 100 & 123 for 110.

[Mountainman]

I had a similar issue with my Mk6 103 TDI. I checked the indicated speed against a Tom Tom GPS.
With the Mk6 I set the cruise to 125klm/h for 110 klm/hr speed limit & drove through the speed traps no problems over 3 years off hwy driving.
With the Mk7 103 TSI its a bit less & the difference is greater at higher speeds.
Cruise set to 67 for 60, 88 for 80, 110 for 100 & 123 for 110.

If I did that with mine I wouldn't have a license now. It is consistently 5km/h above the true speed. Indicating 125 is really 120 and in QLD we'd get booked for that in a 110 zone.

[brad]

If I did that with mine I wouldn't have a license now. It is consistently 5km/h above the true speed. Indicating 125 is really 120 and in QLD we'd get booked for that in a 110 zone.

That would be why you'd double check the true speed using at least one GPS rather than just taking blind advice from a forum.

All our cars are different & the diameter of our tyres can vary markedly from brand-to -brand even if they are the same nominal size.

Martinnw seems to be at the extreme end of innacuracy.