Looking for some guidance. I am thinking of purchasing a new Mini with stock 15 . Then buy larger rims 16 - 17 inch rims and tires for the summer and use the 15's for winter. Going with what I have read at the forum you can buy lighter rims then from factory plus save some money .

What effect does the larger rims have on the calibration of the speedometer and Tachometer.

Or is this a non issue no need to be concerned. Can there be a simple software change to offset larger diameter.

Do they set the car up differently in factory if you order 15 , 16, 17 or 18 " rims to the speedometer or tack.

 

Size of the wheels is basically irrelevant. You get different tire sizes to match the same overall diameter as your stock setup.

You'll notice the size of the sidewall on the tire gets shorter as the diameter of the wheel increases.

A tire in size 195/55/16 or 205/50/16 will give a similar overall tire diameter to your stock 175/65/15, for example. Thus, very little speedometer error and no calibration necessary.

Useful info to give you a better understanding:
http://autorepair.about.com/od/gloss..._plues_one.htm
http://www.yokohamatire.com/utplus.asp