17 to 18" Wheels

[matski]

I changed my 17" Monzas to 18" Monza II's, Spoke to VW yesterday and they said i have to get the speedo recalibrated? Never known of this before is it something I should worry about? Any recommendations?!

Cheers

Oly

[Phil1980]

They are talking bollocks your speedo will just read higher with 18's mine is a few mph out when I compare it to my sat nav,  wouldn't worry about it unless they are going to calibrate it for free.  Are you keeping the 17's?

[matski]

Yer thats what i thought, it could only be a slight difference! So r u saying that the speedo reading will be fast with the 18's? I'm selling the 17's in the classifieds section: http://www.golfgtiforum.co.uk/index.php?topic=171212.0

[Jimp]

If your wheel's rolling radius is the same then it won't change your speedo. If you fitted 18's with huuuuge tyres then it would be out, but with appropriate size tyres it will be fine.

[matski]

Ok, i'll check them out later and compare, how do I know what the rolling radius is?

Thanks

[Jimp]

The best way to get the same size tyres as the factory 18's use.
This site can be handy for double checking:
http://www.miata.net/garage/tirecalc.html

[matski]

Thanks for that. That website says that my speedo is 0.5% out, so when i'm doing 60mph i'm actually do 60.3mph, so its a tiny difference!

Thanks for clearing that up for me.

[nr123]

There will be no difference!! The overall size of the tyre and alloy combined has not changed.
You've gone from a 225/45/17 to a 225/40/18 (hopefully). The reduction in profile compensates for the increased size of the alloy.

[jeynesey]

225/40/18

[Gene Hunt.]

I replaced the standard 17'' monza alloys to Edition 30 alloys & nothing changes other than they look much better.