When you change or buy tyres, you will need information about their size. You will find them easily on the sidewall of each model.
This is a string of characters, e.g. 195/55 R16, where the first number is the cross section width measured between the tyre sidewalls in millimetres. The second value is the height of profile (aspect ratio), i.e. a percentage to tyre width, e.g. 55 is 55% of 195. ”R” indicates the tyre type (R - radial, D - diagonal). The last number denotes the width of a rim in inches.