Speedo reading wrong

[Northy1985]

Does anyone know how I can correct my speedo. Doing 70mph yet clock is reading 80 I know this as I followed my brother on motorway he was doing 70 mine 80. And also wen clock reads 30 I'm doing 28. 40 is 36. 50 is 45 and so on

[doylebros]

I've never done this but these recon it's simple http://forums.tdiclub.com/showthread.php?t=158652

[Northy1985]

I will give it a go it just seems weirdest sits on zero wen off and 30 is not too bad but every 10mph extra adds like 2mph so by time I doing 80 it's close to 70

[dazza]

This was at the end of that thread. Supposedly you can adjust with VCDS.

http://www.myturbodiesel.com/wiki/speedometer-fast-error-adjustment-and-correction-mk5-mk6/

[Northy1985]

Looks too complicated to me lol. I don't have vcds either.

[dazza]

Have a look at the VCDS register i'm sure someone can help for a few beer tokens.

[Northy1985]

Yes mate I will do cheers

[Carpy25]

Do the simple things first are you running the correct size tyres ,are they at the correct pressure , smaller tyres or low pressure will make the speedo under read
All speedos under read but yours is outside the 10% allowed

Rob

[Northy1985]

I'm running 18" wheel with 215/35/18 tyre with 28 psi. Only reason I noticed it was today traveling with the Tom Tom on I was doing 80 but that was reading 74 but my brother following said I was doing 70. So I dropped down to my speedo 70 and he said was just over 60.

[Carpy25]

Your tyre size is down and your pressure is lower than recommend every  revolution less distance will be covered but your reading higher than the speedo  if I'm reading this right

Is your car meant to have 18 " wheels with 225 40 18 tyres or something else as standard

Rob

[Carpy25]

Try this

http://www.wheelcalc.com/

To compare what should be fitted to what you have fitted pressure will play a small part but not hugely


Next do yo have to correct gear box fitted , have you the correct clocks fitted

Rob

[Northy1985]

As far as I know all the clocks etc are correct and the wheels where 18" Monza with 225/40/18. Yeah I am reading higher than I am actually going. The Tom Tom reading 74 car reads 80 but at 30 I'm doing 28 and to every extra 10mph I'm losing 2mph so by 80 I have nearly lost 10mph

[Carpy25]

With the tyres your running using the web site I posted you should be reading about four MPH over so your about 14 MPH out
Think you've covered the easy answers  must be a set up problem as said above  vagcom is your next step I think

Rob

[Northy1985]

I still have the standard wheels so I may aswell try with these just to rule out wheels/tyres problem then I know for sure. Then go from their

[xjay1337]

Reallly over complicating things here loll
The car is fine.
Speed differences are due to tyres/rolling diameter/vcds coding values (some GTI's were off so need changing on vagcom).