Speedo reading wrong

[dronners]

consider it a good anti speeding assistant 

[Scottymon]

I thought Most cars dials were ~10% out when comparing to the Actual speed.

[Northy1985]

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).

Only thing different on mine is the fact front tyres are 215/35/18 rather than the 225/40 standard other than thats car is fine i think the difference is not as bad as my bro said as today i sat at 70 and navigation read 65 then at 80 was 75ish at 30 it reads 28

[Rossimac]

I moved from standard 17" Monzas to 18" Pescaras. Using a 225/40/18 all around, I noticed too that the speedo was out quite badly.

I got my VCDS and started to adjust the Digital Impulse Number. All settings yielded no difference. Still reading high!

[Northy1985]

Am i just better off leaving it and just stop being a pussy and getting on with it or just change front tyres back to 225/40

[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).

Only thing different on mine is the fact front tyres are 215/35/18 rather than the 225/40 standard other than thats car is fine i think the difference is not as bad as my bro said as today i sat at 70 and navigation read 65 then at 80 was 75ish at 30 it reads 28

Well you have changed the rotational diameter of the wheels so of course it would be different.
Your car speedometer is never going to be 100% accurate..

[Northy1985]

I am going to put standard wheels back on and do another test run and see if it goes back to normal ish and then go from there. Only good factor is cant get caught by speed camera

[Scottymon]

Going from:

225 40 18
to
215 35 18

Creates a -4.55% difference in the roll (-29mm)

http://www.tyresave.co.uk/tyresize.html

Coupled with the fact most speedo's are incorrect, usually around 10% I've found, when comparing to the Sat Nav.

[Northy1985]

Another run today and at 80 on clock is 74 on navigation and gps speed 70 is 65 and at 60 is 56. Faster you go the more it goes out 90 is 82

[xjay1337]

Another run today and at 80 on clock is 74 on navigation and gps speed 70 is 65 and at 60 is 56. Faster you go the more it goes out 90 is 82

It's fine!!!!!

[Northy1985]

Another run today and at 80 on clock is 74 on navigation and gps speed 70 is 65 and at 60 is 56. Faster you go the more it goes out 90 is 82

So stop being a pussy then lol
It's fine!!!!!

[Carpy25]

Another run today and at 80 on clock is 74 on navigation and gps speed 70 is 65 and at 60 is 56. Faster you go the more it goes out 90 is 82

that about right its under the 10% so don't worry 

Rob

[Northy1985]

Another run today and at 80 on clock is 74 on navigation and gps speed 70 is 65 and at 60 is 56. Faster you go the more it goes out 90 is 82

that about right its under the 10% so don't worry 

Rob

I will just go with it for now and maybe try standard size tyres to see if it helps but I'm glad I sort of know it's normal ish