Tyre Sizes Explained: Your 101 Guide

Tyre Sizes Explained: Your 101 Guide

You won’t get very far without the correct type of tyres fitted to your vehicle. But what does the tyre size mean? Where can you find it? How do you read it? And why does it matter? 

Here, we answer all of those questions and more. Let’s get started.

How do you read tyre sizes in the UK? 

The good news is that it’s pretty straightforward to find and read your tyre size. Most manufacturers stick to an industry-standard practice of printing the size on the tyre sidewall (the smooth, vertical area on the side of the tyre, located between the edge of the tread and the bead of the tyre). 

There, you’ll see a collection of numbers and letters. Let’s take a look at an example.

Example: What does the tyre size 205/55 R16 91H mean?

At first glance, this might look confusing. But there’s actually a code to crack. The numbers and letters on your tyre break down like this:  

The first three numbers are the width of the tyre in mm. In this case, the tyre is 205mm wide.
The following two numbers are the “profile” of the tyre. In other words, this is the height of the sidewall expressed as a percentage of the width. So, this would be 55% of 205mm, which makes this tyre 112.75mm high.
The first letter is the type of tyre. In this example, R stands for “Radial”. This is the most common type of tyre used today. However, there are other types available. You may see B for “Bias-ply” or D for “Diagonal construction” instead.
The number following the letter is the rim diameter in inches. In the above example, the tyre will fit over a 16-inch rim.
The next number is the tyre’s load index rating. This is the amount of weight each tyre can carry when inflated properly. In our example, the load index of this tyre is 91, which means it can support 615kg. Check the table below for the entire load index:

Tyre Load RatingMax Load65290kg66300kg67307kg68315kg69325kg70335kg71345kg72355kg73365kg74375kg75387kg76400kg77412kg78425kg79437kg80450kg81462kg82475kg83487kg84500kg85515kg86530kg87545kg88560kg89580kg90600kg91615kg92630kg93650kg94670kg95690kg96710kg97730kg98750kg99775kg100800kg101825kg102850kg103875kg104900kg105925kg106950kg107975kg1081000kg

Finally, the last letter is the tyre’s speed rating. This highlights how fast your car can travel safely on these tyres. In this example, H is 130mph. Check the table below for the complete speed ratings:

Speed RatingMax Speed (MPH)Max Speed (KPH)Q99160R106170S112180T118190U124200H130210V149240W168270Y186300

How to find out what tyre sizes fit your car

If you’re buying tyres online, you may have the option of entering your car’s registration number and finding the right tyre specifications for your vehicle. However, that’s not the only option. You can also look at the car itself. 

Depending on the make and model of your vehicle, you may find a diagram inside the door panel of the fuel side door or inside the glove box. This diagram shows the different tyre pressures required to safely drive your car at a sustained speed. Alongside this information, you should see the tyre size range for your car. 

If you can’t find this diagram, your next port of call should be your vehicle’s handbook. 

If you’ve purchased your vehicle secondhand, and you don’t have a handbook “handy,” try searching for it online. 

And if your secondhand car has new wheels fitted (often referred to as “aftermarket” tyres), you may want to consult a local garage or tyre specialist to ensure they’re the correct ones.

Why is it important to choose the right tyre size?

In short, safety. Each vehicle has a recommended rating relating to the performance, longevity, wear and heat resistance of the required tyres. If you install the wrong size and type of tyre, you could make your vehicle more difficult (and dangerous) to drive. 

Plus, fitting incorrectly-sized tyres could invalidate your car insurance. 

If you’re unsure about what size of tyre to purchase for your car, ask a professional for help!

What are the legal requirements for vehicle tyres?

According to the AA, your tyres must meet the following basic legal requirements:

They must be in an acceptable physical conditionThey must be compatible with the other tyres on the carThey must be inflated to the recommended pressureThey must have sufficient tread and depth of tread. The more tread your tyres have, the better the grip on the road and the shorter your stopping distance.

Tyre safety FAQs

What causes my tyres to wear down?

There are several factors that impact your tyre’s wear: 

Driving style – Taking corners too fast or braking harshly can increase wear.Vehicle weight – Tyres on heavier cars will wear down faster. But if you’re carrying excess weight (in your boot or on your roof rack, for example), this could speed up the process.Speed – Regularly driving at high speeds will increase the temperature of your tyres, which will cause them to wear down faster.Pressure – If you’ve over (or under) inflated your tyres, this will cause more damage.

Can age affect my tyres?

Yes. If your car isn’t driven often, your tyres can still degrade to the point where they’re dangerous to use. The rubber breaks down naturally through exposure to the elements. They may last longer if you park your car in a garage, away from the sun and rain. 

How can I tell how old my tyres are?

You can tell the age of your tyres by looking for a code on the tyre sidewall. There you’ll see a collection of letters and numbers, starting with DOT. 

Next to this, you’ll find a four-digit number. The first two numbers denote the week of manufacture. The last two numbers are the year of manufacture. 

For example, a tyre with DOT0821 would be manufactured during the 8th week of 2021. 

If you see a three-digit code instead of a four-digit one, this means your tyres were manufactured before the year 2000. You should replace these immediately. They are no longer safe to drive.

Quickfire summary: Car tyre sizes explained

What do the numbers mean on a tyre size?

The numbers on your tyre highlight the width, height, type, rim diameter and performance capabilities. Purchasing the correct replacement tyre is vitally important, as fitting the wrong size could make your car more difficult and dangerous to drive.

And driving with incorrect tyres could also invalidate your car insurance should you have an accident.

What do tyre widths mean?

The width of a tyre is measured in millimetres, from one sidewall to the other. It’s the first three numbers of the code found on the sidewall. 

In general, the wider the tyre, the more grip you’ll have. 

What is the tyre profile? 

The profile of the tyre is the tyre’s height displayed as a percentage of its width. So, if the code starts 205/55, the tyre’s height is 55% of its width.

A lower profile is typically good for steering performance. However, it also means there’s less cushioning between the rim and the road. This could make for a bumpier ride. 

On the other hand, a higher profile (above 50) provides more protection and offers a more comfortable drive. Choosing a tyre profile often comes down to preference. Do you want better handling or more comfort? 

Also read: