So I found this infomation online and have a question:

+-----------+-------------------+
| TIRE SIZE | DIAMETER |
+-----------+-------------------+
| 195/55-15 | 23.44in (595.5mm) |
| 205/40-17 | 23.46in (595.8mm) |
| 215/50-15 | 23.46in (596.0mm) |
| 215/45-16 | 23.62in (599.9mm) |
| 195/50-16 | 23.68in (601.4mm) |
| 185/60-15 | 23.74in (603.0mm) |
| 215/40-17 | 23.77in (603.8mm) |
| 205/55-15 | 23.88in (606.5mm) |
| 215/35-18 | 23.93in (607.7mm) |
| 175/65-15 | 23.96in (608.5mm) |
| 225/45-16 | 23.97in (608.9mm) |
| 205/50-16 | 24.07in (611.4mm) |
| 225/40-17 | 24.09in (611.8mm) |
| 225/35-18 | 24.20in (614.7mm) |
| 195/60-15 | 24.21in (615.0mm) |
| 205/45-17 | 24.26in (616.3mm) |
| 215/55-15 | 24.31in (617.5mm) |
| 195/55-16 | 24.44in (620.9mm) |
| 215/50-16 | 24.46in (621.4mm) |
| 185/65-15 | 24.47in (621.5mm) |
| 215/45-17 | 24.62in (625.3mm) |
+-----------+-------------------+

Why is it that tires that have the same wheel radius and sidewall measurement but different widths end up deing different diameter?

The sidewall number isn't a measurement, it's a percentage of the width.

Here's an example

205/55 R15

205 = width in mm
55 = height of one sidewall expressed as a % of the width.
15 = diameter of wheel in inches

Diameter = 15 inches + 2 * 55% * 205mm / 25.4mm per inch = 23.88 inches

Ahhhhhhhhhh Thankyou, that explaind alot!!!

isn't it ironic how they mixed up inches and metric in the same
measurement?

why width in mm?
why diameter in inches?

Dave is exactly right. It's the aspect ratio, a percentage of the width expressed in the height of the sidewall. Therefore a 205/60 15 will be taller than a 185/60 15 as 60 percent of 205mm is a larger number than 60 percent of 185mm.

Thanks Dave for that answer.

The variation also helps to give us a variety of tires to choose from that will fit the MINI for different purposes as long as the outer tire diameter is close to the stock size. For most MINIs the stock tire is about 24.4" and we can increase or decrease the outer tire diameter by about 0.5" without creating problems.

Next you look at the width of the tire you want to consider along with the sidewall height ratio. 40 or 45 series tires for performance and 55 or 60 series tires more for comfort and street use with some performance.

Tire companies cannot make all sizes possible and will have to pick and choose what tire sizes would sell for the masses. For some of the tire sizes in your chart very few to no tires exist:
225/40-17
215/55-15

So another question, I just got my brand new S, been wanting one for 3 years and finally got it.

I wanted to get snow chains for it but the manual seems to say that only these tire sizes are allowed for snow chains:

175/65 R15
175/60 R16

Can I put 175/60/R16 tires on my stock R16 R84 Cooper S wheels?

They have 195/55/R16 right now.

Or is this guideline a bit shakey and I can put chains on anyway?

chains will make the overall width wider...that's why
they tell you to use narrow and tall tires.

so, go by their recommendations.

When I search tirerack.com for 175/60-16 tires I get nothing.

You should give Alex@tirerack.com a call and ask about sizes of snow tires to use for your MCS and about the chains. Let us know what you find out.

Yes... that is if you can find them.
Seems to me that is a size that may be available in Europe, but North America... doubtful.

Hiya folks, this is my first post here and I decided to make it a meaningful one. I just ordered my Mini, it wont be here until dec 1st and I can hardly wait!

Myself, I ski and snowboard here in Oregon and I needed to be able to put snow chains on to get up the big hill to the snow parks but when I started searching for chains I found this forum and this thread! YIKES! It freaked me out!

BUT!

I called my dealer and they recommended these guys here

http://www.spikes-spiders.com/

They are called spikes spider and they are made to work just like, actually better than, snow chains with one big difference!

They are made to work with sports cars and other cars like our mini cooper that have no where near enough clearance between the tire and the wheel well wall surface.

They only clip on over the outside of the tire and the tread part covers just the top of the wheel. Nothing on the inside of the tires edge! Too cool!

At $279 for the set they arent cheap, but for those of us that do not like to ride around on snow tires and just need to chain up when the occassion calls for it, these are perfect!

My dealer also told me that the use of these guys will not effect my warranty so I am going to give them a run. I will probubly order then before I even get my mini so I am ready for the ski season. Best of luck and hope this helps! Jeff

Im off to post in the newbie thread now!

Thanls man, I will check them out, I said a similar thing to you, yikes, or maybe it was bulls*@t.

Unlike other states CA requires chains when it is big time in the mountains.

I wonder if these spider spikes count?

And they are more like 350 bucks!!!

From experience running them in the mountains around big bear etc. I know that spider spikes do meet the requirements for chains and or snow tires. I have a history of using them on a saturn SL1. they are for short term use. Just to get you through the snow. absolutley not for pavement or speeds above 30 mph.