Width of the tyre measured in millimetres from sidewall to sidewall. In this example the tyre has a width of 205 mm.
The tyre profile refers to the height of the tyre sidewall as a % of the tyre width. 55 for example is a percentage of the overall tyre width.
The rim measurement is the rim diameter of the tyre. It is a two digit number that can be found just after the letter R on the sidewall.
The speed rating of the tyre indicates the maximum speed that your tyre is legally approved for. This will be represented as a single letter after the wheel size detail.