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Tyre Sizes Guide

Understanding your tyre size can be confusing. Until you’re actually faced with having to replace a tyre, the codes on the sidewall of your tyre may seem like a random collection of numbers, but they actually contain vital information about the tyre size your car needs. Each tyre code is used to identify the size, manufacturer and physical features of the tyre and is displayed in this format 205/55R16. In this guide, we’re going to look at the numbers you should pay attention to on your tyre and what each one relates to when you need to buy new tyres. 

How to read tyre codes

Your tyre code is a sequence of numbers and letters. With so many different tyre codes available, it’s important to know your existing tyre size to ensure you know what size to order when replacing. The most common UK tyre size is 205/55R16, let’s break down what each part of this code means. 

Tyre Width

In this code, the 205 relates to the width of the tyre with the three digits displaying the width in millimetres. A tyre marked with 205 at the start will measure 205mm across the tyre tread from sidewall to sidewall. 

Aspect Ratio

The next two digits on your tyre code are the aspect ratio, or profile height of the tyre sidewall expressed as a percentage of the tyre width. Using the 205/55R16 code, the 55 shows that the aspect ratio of the tyre is 55% of the width. 

Radial

Almost all new tyres manufactured in the UK are radial tyres. This means that they are constructed with cord piles positioned at a 90-degree angle to the direction of travel in order to give the tyre extra strength. The letter R in the tyre code will identify that your tyre is a radial tyre. 

Wheel Diameter

The next two digits on your tyre code identify the size of the wheel rim that the tyre is fitted to, it’s also the diameter of the tyre from bead to bead. In this code 205/55R16, the 16 identifies that the tyre will fit on a 16-inch wheel rim. 

What do the other tyre numbers mean?

Although you typically only need the initial code to identify your tyre size, there are other markings on the tyre that you can familiarise yourself with. 

Tyre load index

The load index represents the maximum load that the tyre can carry when it is inflated to it’s maximum (safe) pressure. For example, if your tyre has the number 97 following the main tyre code, this identifies that it relates to index 97 on a ‘look-up’ table, which is used to determine the load in kg. 

What is the speed rating on tyres?

The speed rating is displayed in the form of a letter and represents the maximum speed that a tyre can carry a load safely. Speed ratings range from A (the lowest) to Y, with H as the exception as it is rated between U and V. As with the load index, each speed rating letter corresponds to a value in km/h. It’s important to note that the maximum speed that your tyre CAN carry does not mean that you can ignore legal speed requirements!

Need help finding the right tyre size? At Tyre Savings, you can search by the size of your tyre or by your vehicle registration. If you have any further questions, get in touch with a member of our team today.