I was looking for winter tire choices to use on stock 8" rims as our winter wheel options are basically non-existant.

The following Michelin Arctic's state that they can be mounted on 8" rims:

225/50/17 section width 10" on 7.0" rim
235/50/17 section width 9.9" on 7.5" rim
235/45/17 section width 9.6" on 8.0" rim (stock)

There is no definition of the section width. I don't think it is the tread width as this is specified by the 225 or 235, right? The section width must be the widest point of the tire when inflated, right? It is usually the mid-point of the tire, the balooning sidewall part. Am I right or wrong on this?

Too bad they don't list section widths mounted on the same width rim for comparison. Is this possible to work out?

I'm considering going with the 225/50/17 on the stock rims...
Yeah, yeah, I don't care about my speedo being a bit off.

 

The section width represents the width of the tire from sidewall to sidewall. For example, a 225 is 225mm wide from sidewall to sidewall. To convert that to inches, divide 225 by 25.4 (mm in an inch) and you get the width in inches. So, a 225 is 8.8" wide.

The sidewall is represented by the 50 designation. This means the sidewall height is 50% the width of the tread.

To see more on calculating tire dimensions, visit our following link:

Calculating Tire Dimensions

 

Thanks for trying to help, but...
I was looking at this document:
http://www.michelinman.com/assets/pd...pilotalpin.pdf

For example, taking the line with the 225/50/17:
225/50/17 states that the section width is 10" on a 7.0" rim (rim range is 6.0" to 8.0"). According to what you wrote above, the section width is going to be 225/25.4 = 8.8". When comparing to what the sheet has, it leaves a difference of 1.2", which is quite significant.

Another example, the 235/45/17 has section width of 9.6" on 8" rim. According to your math, 235/25.4 = 9.2". This is lot more resoanable giving a difference of 0.4".

Why is there such a huge difference in the first example? Is there a way to standardize both tire sizes to the same rim width for comparison?

Am I right to assume that the section width and the tread width will be narrower on the 225/50/17 than the 235/45/17 when mounted on the same rim? Theoretically, the 225 should be narrower by 10mm (or 1cm or 0.4"), right? But what would be the difference in real life?

 

The formula I provided is a general way to find the section width of a tire. (sorry for the confusion) Manufactures design a tollerance into their tires for fitment purposes. It is not uncommon for the same size tire to have different rim tollerance or sections width in different brands. This allows the manufacture to gain more versitality in performance and fitment.

You are correct, the 225 will be a physically narrower tire than the 235's. Their rim fitting range might be similar, but they are physically different widths. This will also result in a narrower tread slab, or a smaller footprint on the ground.

 

Very true! For example, a set of Nitto drag radials 225's stacked up on the ground are taller than a stack of 245's from other brands. They are so much wider for the "stated" size that they can actually cause fitment issues on cars that would be able to run 225's from another brand with no problems at all.

Keith