I'm seriously thinking of going to 16" or 17" wheels. If I do this, I know the speedo is affected. How is this adjusted? Is this something MINI has to adjust, or can I do it myself? And if it is a DIY job, any experiences to share? Thanks for the info.

Jason

 

Are you sure that the overall circumference is changed, I think they are talking about the rim size, that changes how much rim and rubber you have, not the overall size of the wheel. I may be wrong... There is a number that relates to the ratio of width to height of the rubber of the tire, and that changes as you go to larger diameter rims.

 

Shaguar 1 has it right. If you check the size of the TIRES as the wheel diameter goes from 15" to 17", you find the following tire sizes:

15" wheel; tires: 175/65 R15
16" wheel; tires: 195/55 R16
17" wheel; tires: 205/45 R17

What MINI does is to vary the "aspect ratio" (65, 55, and 45; above) and the tire width (175mm, 195mm, and 205mm, above) to keep the rolling radius "fixed". That way, there is no (or minimal) impact on your speedo (and ABS, etc). Simply put, as the WHEEL diameter gets larger, the tire SIDEWALL gets smaller.

I've copied an example from Tire Rack's web site (below, for a 185/60HR14 tire) that illustrates these calculations:

The first number is the width of the tire in millimeters, measured from sidewall to sidewall. To convert to inches, divide by 25.4 In the example above, the width is 185mm or 7.28".

The second number is the aspect ratio. This is a ratio of sidewall height to width. In the example above, the tire is 7.28" wide, multiply that by the aspect ratio to find the height of one sidewall. In this case, 185x0.60=111mm or 7.28"x0.60=4.36".

The last number is the diameter of the wheel in inches.

To figure the outside diameter of a tire, take the sidewall height and multiply by 2,(remember that the diameter is made up of 2 sidewalls, the one above the wheel, and the one below the wheel) and add the diameter of the wheel to get your answer.

Example...185/60R14 85H or 185/60HR14

185mm x .60=111mm x 2=222mm + 355.6mm(14&quot= 577.6mm or 22.74"

You can "tweek" the aspect ratio and tire width to achieve the desired (fixed) outside diameter of 22.74" (for this hypothetical case) as one increases the wheel diameter (from 14" to 15", etc).

I hope this helped!

(ps: in REAL life, the manufacturers measure the tire width differently sometimes, and so you have to be a little carefull!)

 

Thanks for the info, guys! So I don't have to worry about the speedo. That's even better than I was hoping for! (Learned a thing or two as well!)

Jason