The numbers and letters on your tyres can be puzzling. The sidewall of the typical tyre is imprinted with many codes and numbers that are used to identify the size and physical features of that tyre as well as details relating to its make & manufacture. Most of these tyre markings are of little or no importance to you while others are essential when it comes to choosing a replacement tyre.

If you are looking for new tyres you should familiarise yourself with the following tyre markings.

Tyre Size

Example 215/60R15

215 is the width of the tyre in millimetres.

60 is the aspect ration of tyre profile.

R means it is a radial construction.

15 is the diameter of the rim of the wheel in inches. 

Tyre Size 

Your tyre size can be found on the sidewall of your current tyre and is shown as numbers and letters. The most common Irish tyre is 206/55R16, there are many different types it is important to check your vehicle handbook and current tyres to ensure the right tyre size.

Tyre Width

The first three digits. This is the width of the tyre in millimetres. Tyres marked 225 will be 255mm from sidewall to sidewall.

Aspect ratio

The 4th and 5th digits of the tyre code that immediately follow the tyre width. The aspect ratio or profile height of the tyre sidewall is expressed as a percentage of the tyre width. An example aspect ratio of 55 means that the profile height of the tyre is 55% of its width.


Radial tyres are marked with the letter R. Radial tyres are constructed with the cord piles positioned at a 90-degree angle to the direction of travel to give the tyre additional strength. Nearly every new tyre manufactured today is a radial tyre. 

Wheel diameter

The next two digits represent the size of the wheel rim that the tyre can be fitted to. It is also the diameter of the tyre from bead to bead. So a tyre marked 16 will fit on a 16-inch wheel rim.

Examples of Tyre Sizes

Width: 185 Profile: 65 Diameter: 14

Width: 195 Profile: 65 Diameter 15

Width: 195 Profile 55 Diameter 15