Buying tyres can seem like trying to understand a foreign language, but the markings on the tyres all carry important information that is critical to making the right decision when your old tyres need replacing.
Found on the side of the tyre, called the tyre sidewall, these letters and numbers refer to the width, height, diameter, load and speed parameters of your tyres. The numbers are a confusing mess of millimetres, inches, percentages and other codes, which can make it all a bit bewildering.
Our helpful tyre markings guide clearly explains all the key numbers and letters, without any jargon or sales spiel. When buying tyres, a tyre shop may give you a choice of different sizes or specifications that will fit your car, so this guide will help you make the right choice.
Tyre width is measured in millimetres (mm) and for the vast majority of car tyres always ends with the number ‘5’.
Why is this important? Tyre width is important as it can affect both your car’s performance and how economical it is with fuel. The amount of rubber that is in contact with the road (called the contact patch) impacts your tyres grip and rolling resistance. The larger the contact patch, the greater the grip but the higher the rolling resistance, resulting in lower fuel economy.
Aspect ratio, sometimes referred to as ‘profile’, is essentially the height of the tyre’s sidewall outward from the rim represented as a percentage of the tyre’s width. So, if a tyre has an aspect ratio of 65, that means the height of the tyre’s sidewall is 65% of the tyre’s width.
Why is this important? Low profile tyres (where the profile is lower than 50%) require the sidewall to be stiffer, while higher profile sidewalls (more than 50%) provide more flex to cushion you over bumps and potholes. As such, higher profile tyres tend to provide more comfort. Lower profile tyres, meanwhile, tend to provide better handling as the stiffer sidewall means that the tyre doesn’t move around as much when cornering.
In recent years, however, low profile tyres (which allow larger alloys wheels to be fitted) are more often chosen for aesthetics rather than their performance benefit.
Rim diameter is the diameter of the metal wheel that fits in the centre of the tyre. The majority of car wheels are measured in whole inches and generally range from 12” to 22”.
Why is this important? Larger diameter wheels and tyres are preferable for high performance vehicles as the tread has less pronounced curvature. This creates a larger contact patch and increased grip, which is important for powerful cars and for maximising performance when cornering. In combination with low profile tyres, large diameter wheels are now fitted onto most modern cars more for aesthetic than performance reasons.
While the number denotes the rim diameter in inches, the letter before it tells us the type of construction used in the casing of the tyre. In this case, ‘R’ stands for Radial construction, which is pretty much universal for modern car tyres. Other examples include “B” for Bias-ply or “D” for Diagonal construction, usually only seen on cars from the 1960s or earlier.
Using the “tyre load index table” below, your tyre’s load index indicates the maximum weight that your tyre can safely support. This way of measuring a tyre’s weight capacity is relatively modern and was introduced to provide a more consistent method of comparing tyres.
Why is this important? Putting more weight on your tyres than they can safely handle is dangerous. It can make the car unstable and can lead to a tyre failing in a blowout.
The tyres on passenger cars usually have a load index between 75 and 104, each index number having a specific corresponding load weight that the tyre can safely drive with.
|Load Index||Kilograms (kg)|
|Load Index||Kilograms (kg)|
|Load Index||Kilograms (kg)|
Speed index is a letter(s) which relates to the table on the left. It represents the maximum speed that your tyre can safely run for a maximum of 10 minutes while supporting the maximum weight indicated by its load index. Every vehicle has a minimum required speed index as required by the manufacturer.
Why is this important? Like excess weight, driving at a speed beyond the safe limit of a tyre’s design can be dangerous. The tyre will not handle well at higher speeds and the excess load can cause it to fail – and at motorway speeds, that could lead to a serious accident.
It is acceptable, legal and safe to fit a higher speed index tyre than originally fitted, but not a lower speed index. It may also invalidate your insurance.
Winter tyres are an exception and it is permitted by most vehicle manufacturers to reduce the speed index fitted by one step.
|Speed index symbol||Approx. max mph|
Brand name – Often the largest marking on the tyre, the brand which designed and manufactured the tyre will always proudly display its name and/or logo.
Tyre name or pattern name – The tyre is likely to have its own product name as a marking too, denoting what product range it comes from or the type of tread pattern it has.
Country of manufacture – In some cases, the name of the country where the tyre was manufactured will be marked on the tyre wall, telling you where your tyre exactly came from.
Manufacturing date code – The tyre will sometimes be marked with its manufacture date, displayed as a long set of letters and numbers like this ‘DOTXXXXXXXX1320’. The last four numbers relate to the manufacture date – ‘1017’ means that the tyre was made in the 13th week of 2020.
European ECE Type Approval – Appearing as the letter ‘E’ and a number encased in a circle, this mark indicates that the tyre meets European safety standards. The number tells you what country that the tyre was tested in to meet those standards – ’11’ means it was tested and approved in the UK.
‘TWI’ – You may find these letters in the grooves to the tyre treads, instead of the sidewall. ‘TWI’ stands for ‘Tyre Wear Indicator’ and if you can see this marking clearly it means that your tyre is pretty worn and needs changing.
‘SSR’ – Tyres with this sidewall marking are ‘Self-Supporting Run-flat’ tyres that can continue to be used in the event of pressure loss thanks to its reinforced walls.
‘MOE’ – This marking denotes another run-flat tyre, but for Mercedes-Benz drivers (Mercedes Original Equipment tyre).
‘M+S’ – Nope, not Marks & Spencer. A marking like this tells you that your tyre is ideal for mud and snow conditions.
Some tyres – particularly performance tyres – will also have codes to show that they are specifically designed to suit a particular car manufacturer’s requirements. For example, a tyre manufacturer may have different versions of a particular tyre to suit Audi, BMW and Mercedes-Benz requirements. These don’t usually make a massive difference to the tyre’s specification, although they do allow car manufacturers and tyre companies to charge a significant extra premium for them.
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This article has been updated in May 2022, and was originally published in September 2014.