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Understanding Car Tyre Markings – A Beginners Guide

When most of us look at the tyres on our car we just see numbers and letters and look away again in confusion. Today, we are going to explain to you what the different numbers and letters actually mean.

Firstly, you will always find them on the outer sidewall of the tyre, on some tyres there is more information included such as technical characteristics and approvals etc. But for today we are going to focus on the basics.

How to read your tyre markings

A: Tyre width

The tyre width is measured from sidewall to sidewall but excluding any raised lettering or rim protectors.

Safety tip: Tyre width is important as it can affect both your car’s performance and how economical it is to run.

B: Section Height

These two digits represent the height of the tyre’s sidewall as a percentage of the tyre width.

Safety tip: Check tyre pressures regularly. Tyres with a low profile can sometimes look normal even with dangerously low pressure.

C: Rim Diameter

The letter R stands for radial – the tyre of tyre fitting to your car. Crossply and Belted Crossply will usually be marked with a dash replacing the letter R. The number is the diameter of the tyre’s inner rim or the size of your wheel rim. This is measured in inches. In this example the diameter is 55 inches.

Safety tip: It is vital to fix the correct size wheel-to-tyre combination in order to obtain optimum performance from the tyre.

D: Load Index

In our example, 91 is a code for the maximum weight (in kg) that your tyre can safely support. Car tyres have load indices that range from 75 to 105, where each numeric value equates to a specific load capacity. You can use one of the online load tables to work out what is the maximum load your tyre can take.

Safety tip: Avoiding exceeding this weight as it can result in steering instability and even rupture.

E: Speed index

Speed index is a letter which refers to the table on the left. the last letter indicates the maximum speed for the tyre at full load. In this example the tyre has the letter V which means the top speed is 149 mph.

Safety tip: It is really important to check your speed index as choosing a tyre with a rating too low for your car can invalidate your insurance.

Tyre markings – video

In this video, Tyreland co-owner Keith Duffy, explains how to read the markings on your tyre’s sidewall.