Knowing how to check tyre sizes is an important part of choosing the correct tyres for your car. The size affects whether a tyre is suitable for the wheel and vehicle, while the load index and speed rating are also important when selecting replacements.
If you’re replacing tyres yourself, knowing how to check tyre sizes correctly can help you avoid ordering the wrong specification.
The information can look confusing at first. A marking such as 205/55 R16 91V contains several different pieces of information about the tyre, including its width, aspect ratio, construction, wheel diameter, load capacity and speed capability.
This guide explains how to check tyre sizes, where to find the correct information for your vehicle and what the different numbers and letters on a tyre mean.
Using the correct tyres is important for your vehicle’s handling, braking, stability and overall safety.
Your car manufacturer specifies suitable tyre sizes and other characteristics for the vehicle. Depending on the model and specification, a car may have different approved tyre sizes, and some vehicles use different sizes on the front and rear axles.
Fitting an unsuitable tyre can affect the way the vehicle handles and may also create clearance or compatibility problems.
This is why learning how to check tyre sizes should involve more than simply looking at the numbers on the tyre currently fitted to your car. The existing tyres may not necessarily be the correct specification, particularly if the vehicle has previously been fitted with aftermarket wheels or replacement tyres.
The safest approach is to check the vehicle manufacturer’s recommended specification before buying replacement tyres.
Taking a few minutes to learn how to check tyre sizes can help you avoid choosing an unsuitable replacement.
There are several straightforward ways to learn how to check tyre sizes before ordering replacement tyres.
Your vehicle handbook should be one of the first places you look when learning how to check tyre sizes.
It may list the approved tyre sizes for your particular model, along with recommended tyre pressures and, in some cases, different specifications for different wheel sizes.
Pay particular attention to whether your car has different approved sizes for different trim levels or wheel options.
Many vehicles have a tyre information label or placard showing recommended tyre pressures and sometimes the approved tyre sizes.
Depending on the vehicle, this information may be found on the driver’s door frame, door pillar, fuel filler flap or another area specified by the manufacturer.
The handbook or manufacturer’s information should take priority if you’re unsure.
The sidewall of the tyre contains its size and service information.
For example, you might see:
205/55 R16 91V
Once you know how to check tyre sizes, these markings become much easier to understand.
Understanding the markings makes it much easier to learn how to check tyre sizes yourself.
The first number represents the tyre’s nominal width in millimetres.
In this example, 205 means the tyre has a nominal width of 205mm.
The second number is the tyre’s aspect ratio.
A 55 means the sidewall height is 55% of the tyre’s nominal width.
The aspect ratio is important because changing it can alter the overall dimensions of the tyre and therefore affect the vehicle’s characteristics.
The R indicates radial construction.
Most modern passenger-car tyres use radial construction.
The number after the construction marking represents the diameter of the wheel that the tyre is designed to fit.
In this example, 16 means the tyre is designed for a 16-inch wheel.
The wheel diameter is not the same as the overall diameter of the complete tyre.
Once you understand these markings, knowing how to check tyre sizes becomes much easier whenever you need to replace or compare tyres.
The numbers and letters after the basic tyre size are also important when you learn how to check tyre sizes.
In 205/55 R16 91V, the 91 is the load index and the V is the speed symbol.
The load index indicates the maximum load the tyre is designed to carry under specified conditions.
You should make sure replacement tyres have a load index that is appropriate for your vehicle and, where applicable, meets or exceeds the manufacturer’s specification.
TyreSafe recommends fitting tyres with a load index at least equal to that originally specified by the vehicle manufacturer.
The load index is not simply the maximum weight of the entire vehicle. It relates to the load capacity of each individual tyre.
If you’re unsure which load index your vehicle requires, check the manufacturer’s information rather than guessing.
The speed rating is represented by a letter and indicates the maximum approved speed of the tyre when operating within its specified load conditions.
For example, V is a particular speed rating, while higher ratings use different letters.
The correct speed rating is important because it forms part of the tyre specification chosen by the vehicle manufacturer. TyreSafe recommends fitting tyres with a speed capability at least equal to that originally specified.
Don’t choose a tyre based on the speed rating alone. The complete tyre specification needs to be suitable for your vehicle.
A marking such as:
205/55 R16 91V
means:
Tyres can have additional markings as well. Depending on the tyre, you may see information relating to reinforced or extra-load construction, direction of rotation, asymmetric fitment, manufacturer approvals and other characteristics.
This is why it’s important to look at the complete marking rather than only the first four elements when learning how to check tyre sizes.
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Some vehicles use the same tyre size on all four wheels, while others have a staggered setup with different sizes on the front and rear.
This is particularly common on some performance cars and vehicles with larger wheels.
For example, a vehicle might use a narrower tyre at the front and a wider tyre at the rear.
Never assume that all four tyres should have the same size simply because many cars do. Check the manufacturer’s recommended specification for each axle.
Tyres fitted to the same axle also need to meet the applicable requirements for size and construction.
Knowing how to check tyre sizes for each axle is therefore particularly important on vehicles with staggered wheel and tyre setups.
If you’re unsure how to check tyre sizes, following these steps will help you confirm the correct specification before placing an order.
These simple checks make it easier to understand how to check tyre sizes before you compare prices or purchase new tyres.
Start with the vehicle handbook, manufacturer’s information or tyre placard.
Make a note of the approved tyre size and the required load and speed ratings.
Look at the sidewall of the tyre currently fitted to the vehicle and compare the marking with the manufacturer’s recommended specification.
Don’t automatically assume the existing tyre is correct if the vehicle has aftermarket wheels or you are unsure about its history.
If your vehicle has different front and rear tyre specifications, make sure you’re ordering the correct size for the correct axle.
Don’t stop after finding the basic size.
Check the load index, speed rating and any additional manufacturer-specific requirements that apply to your vehicle.
Tyre pressure is not part of the tyre size.
Your recommended pressures are normally provided by the vehicle manufacturer and may vary depending on the load being carried.
The Highway Code states that tyres must be correctly inflated to the vehicle manufacturer’s specification for the load being carried. GOV.UK also recommends checking tyre pressures regularly, with checks carried out when the tyres are cold.
Knowing how to check tyre sizes is only the first step. Once you’ve established the correct specification, you still need to choose suitable tyres.
Think about how and where you normally drive.
A car used mainly for commuting on motorways may have different requirements from one regularly driven on rural roads or in areas where winter conditions are more common.
For most UK motorists, the priority should be choosing a quality tyre that matches the vehicle manufacturer’s specification and is appropriate for normal driving conditions.
Tyre performance can vary considerably between different products of the same size.
When comparing tyres, consider factors such as wet grip, rolling resistance, noise and overall performance.
New tyres sold in the UK and covered by the relevant tyre labelling requirements carry information that can help consumers compare certain performance characteristics.
Buying the cheapest tyre available isn’t always the best approach.
Tyres are one of the most important safety components on your vehicle, so consider the tyre’s specification, manufacturer, performance characteristics and suitability for your driving needs.
That doesn’t mean you have to buy the most expensive tyre either. There are often several suitable options at different prices.
Some vehicles have specific tyre requirements or manufacturer-approved tyres.
If you’re unsure, ask a reputable tyre retailer or qualified technician to confirm the correct specification before purchasing.
Learning how to check tyre sizes is useful when buying tyres, but regular tyre checks are equally important once they’re fitted.
Check your tyres for:
For cars, light vans and light trailers in Great Britain, the legal minimum tread depth is 1.6mm across the central three-quarters of the tread and around the entire circumference.
However, don’t wait until a tyre reaches the legal limit before considering replacement. If you notice significant wear, damage or deterioration, have the tyre inspected by a suitable professional.
It’s also worth checking tyre pressures regularly. Incorrect pressures can affect handling, braking, tyre wear and fuel consumption.
For more general advice on preparing your vehicle for different conditions, see our guide to summer driving and our winter car preparation guide.
If you can’t find the information you need, don’t guess.
Start with the vehicle handbook or manufacturer’s information. You can also contact a reputable tyre retailer with your vehicle’s make, model, registration and specification.
If you’re unsure about the correct tyre size or need help choosing suitable tyres, Rednal Tyres can provide tyre advice and help you find the right tyres for your vehicle.
A professional can help confirm the correct tyre size and associated load and speed ratings.
You should also seek professional advice if the vehicle has non-standard wheels, suspension modifications or other changes that could affect tyre fitment.
If you’re buying a used car, checking the tyres can also tell you whether the car is fitted with the expected wheel and tyre specification. It can be worth checking all four tyres rather than assuming they match.
Taking the time to learn how to check tyre sizes can save you from buying tyres that aren’t suitable for your vehicle.
Knowing how to check tyre sizes makes buying replacement tyres much easier and can help you avoid ordering an unsuitable tyre.
Start with the vehicle manufacturer’s recommended specification, then compare it with the markings on the tyre sidewall.
Remember that the basic size is only part of the information. The load index, speed rating and any additional manufacturer requirements can also be important.
Don’t assume that the tyres currently fitted are necessarily the correct specification, particularly if the car has aftermarket wheels or a history of modifications.
Knowing how to check tyre sizes correctly can help you avoid buying tyres with the wrong specifications.
If you’re unsure, speak to a reputable tyre retailer or qualified professional before buying.
Keeping your tyres correctly inflated, checking them regularly for damage and wear, and replacing them when necessary are all important parts of maintaining a safe and roadworthy vehicle. The GOV.UK guidance also recommends following your vehicle handbook for tyre maintenance and specifications.
By taking a few minutes to check the complete specification rather than relying on the tyre width and wheel diameter alone, you can make a much more informed decision when replacing your car tyres.
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