speedo calibration help pls

[boldy147]

i have just bought a mk2 golf gti and i have noticed that because it has 17" wheels on it the  sppedo is not calibrated for these wheels  , can someone please tell me how i go about calibrating the speedo thanks  jason

[jv]

if it has the correct size tyres on the 17's then nothing needs doing

[boldy147]

hi

IT has 205/40 ZR17 84W on it , i know the speedo is out because there is no way i am going as fast as it reads , any other ideas pls

thanks

[MowatGTI]

I am probably wrong in saying this, but surely with the bigger wheels, the speedo would show a slower speed than what you are actually doing?

40 profile too, so surely the diameter is just larger than standard.

Im probably wrong mind.......

[jv]

bigger wheels, correct lower profile tyres equals same(ish) overall rolling radius.

they are the right size tyres for 17's so if the speedo is miles out the problem is elsewhere me thinks.

[Uruk Hai]

Have a look at this, might help ?

http://www.miata.net/garage/tirecalcold.html

[DarnPB]

If in doubt, contact speedy cables. They have a website so do a google on it. They do calibration for speedo's fitted to kitcars and can issue a calibration certificate that is recognised by the ministery of transport as if required.

[raferackstraw]

hi mate i would check you have the correct speedo drive gear on the end of the cable first

does the speedo needle move back and forth when at high speed as this could indicate that the spring in the back of the dial is fooked

try borrowing a sat nav as this will show your true speed

[boldy147]

hi

thanks all for your suggestions , just one more thing i have noticed  . the speedo in my golf is a 140 mph speedo but shouldnt the speedo in a 8v 1990 gti be a 120mph speedo . Is it possible that this is the problem

thanks again

jason

[boldy147]

sorry i have just discovered there was a 140 mph speedo on the 8v gti , what concerns me is that from the look of the 120mph speed and the way my speedo goes up the separation of 120 mph speedo looks as if it would be correct