The size of a tyre is printed onto the side of the tyre – on the area known as the sidewall. When looking for the size, you will see that it is made up of a series of numbers and letters.
In the above example, each section breaks down as follows:
205 - Width of the tyre in millimetres
55 - Height of the tyre sidewall as a percentage of the width. In this case 55%. Also known as the aspect ratio.
R16 - The diameter of the tyre's inner rim in inches
91 - Load Rating of the Tyre.
V - Speed Rating. Indicates the maximum speed for the tyre when at full load.