The tyre size is indicated on the sidewall of a tyre in the form of a sequence of characters, e.g. 155/65 R14, where the first number is the cross section width measured between the sides of a tyre in millimetres.
The second number in tyre size is the height of profile (aspect ratio), i.e. the percentage to tyre width. ”R” indicates the tyre type (R - radial, D - diagonal).
The last number denotes the width of a rim in inches. Knowing the tyre size is essential when making the purchase.