hey everyone i am in the market for a set of 18' wheels to put on my A3 and am just wondering with the bigger wheels on the car will it in anyway affect the cruise control reading of the speed that im doing?

i mean will the speedo be a few mph's out or would there be no difference at all have heard it mite make a difference but said id ask just to be sure before i go out and buy my alloys

if anyone knows can you get back to me thanks [8D]

[IMG]local://upfiles/20336/02C36DD1A57943C48F4576E34BA7D159.jpg[/IMG]

 

If you go for bigger wheels, you will need tyres with a lower profile, so that their overall (outer) diameter is the same as standard. Otherwise the speedo will read a speed that is incorrect.

Vistit the link below to help you choose tyre profiles:

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

 

The best fit to the stock diameter (225/45-17 for Sport or Premium package) is 225/40-18, representing a 0.46% increase. Given factors such as tire pressure and tire manufacturer measurements, that is a negligible difference.

 

thanks for the reply. ill have a look around for the correct offset and tyre size now

 

Notice from your spelling that you guys are probably British. The information in my last post is based on my A3, a US sportback (5-door) model. Not sure that the ones across the pond aren't a bit different. Anyway, the stock offset is +56mm. From what I have read and calculated, the lowest offset one can use should be +45mm, if one maintains the stock wheel width of 7.5" or go bigger with an 8" wide wheel. I think with any lower offset (e.g., +35mm VW wheels) even if there is no rubbing, the wheel and tire will stick out of the wheel well.

I have also read somewhere else that the ECU can be reflashed with different tire specs to maintain correct speedo and odo readings.