A question often asked relates to tyre sizes and what they mean as there are several methods used to identify the tyre size. I have found a very good guide Tyre Sizes Explained Note the website the link takes you to has the following regarding copright, hence I have only given a a link.
The author and copyright holder of this material is Tyre-Rite Ltd.
Copying and reproduction is strictly forbidden.
It gives examples and shows pitfalls of misunderstanding what they all mean.