What does the writing on a car tyre mean?

Published: 12 August 2022

You may have noticed that there are a lot of letters and numbers on the side of a tyre. Many of these are just branding for the tyre’s make and model, but there’s a lot of important information there as well. While different tyre manufacturers put different information on their tyres, there are some key details that you’ll see on every tyre which are useful and important to understand.

When it comes time to buy new tyres, figuring out which ones you need can get pretty complicated. Thankfully, retailers will do a lot of the work for you in working out which ones will suit your car – just ask, and they can recommend options. 

But if you do want to know exactly what all the writing on your tyres means, buckle up and read on.

The image at the top of this page may appear to show a random collection of numbers and letters, but it actually is telling you what size the tyre is and what kind of car it’s suitable for.

Here’s the sequence in full:

225/55 ZR17 101W

Let’s break down all the information that’s given there.

The first element of the sequence tells you the tyre’s width in millimetres. So this tyre is 225 millimetres wide, measured between the inner edges of the tyre, where it meets the wheel.

The width tells you how wide a wheel the tyre will fit. The narrowest car tyres are less than 100mm wide and are fitted to low-powered vintage cars. The widest car tyres measure more than 500mm and are used on certain types of road-legal race cars, such as dragsters. Most modern cars use tyres between 180mm and 250mm wide.

The width of tyre your car needs is linked to how much power its engine has. Wider tyres have a bigger ‘contact patch’ – the area of the tyre that’s in contact with the road. The bigger the contact patch, the more power a tyre can transfer to the road without slipping. That’s why dragsters, which can have a bhp of more than 3,000, need such wide tyres.

The second element of the sequence, seen after the backslash, is known as the ‘profile’ of the tyre. It’s also known as the ‘aspect ratio’ because it’s the depth of the tyre sidewall (the distance from where the tyre meets the wheel to where it meets the road) expressed as a percentage of the tyre width. Still with us? Let’s break it down a bit more. In our example, the aspect ratio is 55 percent of the 225mm width, which equates to a depth of 123.75mm. The tyres on most modern cars have an aspect ratio of around 50%.

Why is this important? Well, for two reasons. First, it affects how much grip a tyre can generate in corners. A tyre with a deeper sidewall flexes more when going round a corner, which can reduce grip. High-performance cars have tyres with lower sidewalls, known as low-profile tyres, because they flex less.   

Your tyre’s profile also affects comfort. Tyres are the first component in your car’s suspension system because they’re the first point of contact with any bumps in the road. A tyre with a higher profile – a deeper sidewall – has more air in it, and is better able to absorb those bumps and give you a more comfortable ride.

Car manufacturers choose the tyre sizes fitted to their cars, aiming to give a balance between grip, comfort and style depending on the type of car and who is likely to buy it. (Some people prefer the look of low-profile tyres and large wheels.)

The third element refers either to your tyre’s speed rating or to how your tyre was made. A speed rating indicates the maximum speed that you can drive with that tyre: in our example the speed rating is ZR, which means the tyre is suitable for speeds of up to 150mph-plus. That’s more than fast enough for most cars, but many high-performance cars need a tyre with an even higher speed rating so they can be driven at their maximum speeds (where conditions and local laws allow).

If your tyre has a speed rating other than ZR, it’ll be a letter from A to Y and given at the end of the sequence (we’ll cover that in more detail a bit later in this article). On those tyres, you’ll usually see R after the aspect ratio.

Rather than referring to the speed rating, this R indicates that the tyre has a ‘radial’ construction – layers of rubber with metal strands running through them. Just about every modern car tyre is made this way. Some vintage and classic cars can feature another type, called cross-ply tyres, but they’re rare.

The fourth element gives the diameter (in inches) of the wheel that the tyre will fit on. In our example, that’s 17 inches. Note that wheels come in a huge range of diameters.

The fifth element is your tyre’s weight rating, which indicates the maximum weight the tyre can handle. The higher the number, the more weight the tyre can support. In our example, 101 corresponds to a weight of 825kg. Multiply that by the four tyres on the car, and the tyre is suitable for a car that weighs in total no more than 3,300kg.

The weight rating of the tyres fitted to any car needs to be high enough to accommodate the car’s maximum gross vehicle weight (MGVW). That’s the weight of the car itself plus a full tank of fuel, a full load of passengers and the maximum weight that can go in the boot. You can find your car’s MGVW in your owner’s manual or by searching online.  

If the weight rating of a tyre is too low for your car, the tyre is more likely to fail. If the rating is too high, the tyre may not generate enough traction and grip for you to drive safely. So try to ensure the ratings of the tyres you choose add up to a figure as close as possible to the MGVW.  

Not all tyres have a weight rating. There’s no particular rule for which tyres do or don’t. If the tyres on your car don’t show a weight rating, you can usually find it by searching for the tyre’s make, model and size online.

We’ve already seen that ZR gives a generic speed rating for some tyres. However, the last element in the sequence gives the specific speed rating for all tyres. These are categorised from A-Z, where (broadly) the higher the letter means a higher speed rating. In this example, the rating is W, which indicates that the tyre is suitable for a maximum speed of 168mph. Go any faster than that and the tyre is more likely to fail. The tyres on all cars have a speed rating that far exceeds the maximum speed the car is capable of doing because it provides a greater safety margin.

This sequence of numbers and letters must match exactly on all the tyres fitted to your car because mismatched tyres can make a car less safe to drive. If even just one of your tyres has a weight rating that’s too low, it will perform differently to the other tyres, potentially making the car less safe to drive. 

If you want to make sure your car is fitted with the correct tyres, you can search online by its make and model or consult a tyre retailer. You’ll also be asked for the sequence if you order new tyres for your car online.  

But we’re not finished. There’s still more important information given on the side of a tyre, as shown in the image below.

The date code tells you when the tyre was made. In this example, the code is 3520.

The number 35 refers to the week of the year when the tyre was made – in this case, week 35 (late August). The code for the week runs from 01 to 52 for every year starting in January.

The number 20 refers to the year when the tyre was made, in this case, 2020. 21 is the code for 2021, 22 is the code for 2022 and so on.

It’s important to be aware of the age of your car’s tyres because they degrade as they age. Old rubber hardens, providing less traction and grip, making your car less safe to drive. Older tyres are also more likely to become damaged or even break apart. There are no hard and fast rules about how old a car’s tyres can be, but experts recommend that you don’t use tyres that are more than 10 years old.

Yet more information about a tyre is given on its label, in accordance with European Union law (which remains in force post-Brexit). Each tyre is given a rating for the impact it has on a car’s fuel efficiency, how safe it is when driving in wet weather and how much noise it generates. The rating scale runs from A to E for fuel efficiency and wet-weather driving and A to C for noise. A is the best rating.

Depending on your priorities, you may be willing to accept, for instance, a lower wet-weather rating for a higher fuel-efficiency rating. If you just want a good all-rounder, look for a tyre that scores at least Bs and Cs across the board.

Tyres that score As across the board are quite rare and can be expensive because they are difficult to design and make. That’s because a tyre with a high level of wet-weather grip will tend not to be very efficient – grip is friction and an engine has to work harder to overcome higher levels of friction. Likewise, a tyre with a high level of grip generally has a larger contact patch which will generate more noise as it rolls along the road.

A removable label with all the information is put on every tyre when it’s made, although it’s usually taken off when it’s fitted to a car. However, tyre retailers must make the label’s information available to customers before they buy a tyre. Online retailers will always display the label information alongside a specific tyre and it’s usually very easy to compare stats across those that are right for your car.

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