What do tyre sizes mean?
A tyre's sidewall has a series of digits and letters. For example, 205/55 R16 91V reveals width, aspect ratio, diameter of the wheel, weight capacity and speed potential. You can decode your tyre size with this free tyre size calculator, then find the correct tyres for your vehicle or search tyres by manufacturer.
Outer sidewall of the tyre
The complete size of the tyre is etched into the outer sidewall.
Six parts of tyre sizes
Width, aspect ratio, construction, diameter of the rim, weight capacity and speed potential.
Tyre size that fits your car
Use the exact size that your vehicle manufacturer suggests to ensure a proper and safe fit.
Tyre size location
The outer sidewall of the tyre shows a combination of digits and letters, like this:
205/55 R16 91V
↑ This is your tyre size
Decode your tyre size
Enter the digits and letters exactly as they are displayed on the tyre sidewall, then click Decode.
Popular sizes
Understanding tyre sizes
Though the marking systems may be different, tyre sizes are generally the same everywhere. For example, take 205/55 R16 91V. The first three digits signify the width of the tyre in mm, so 205 refers to the tyre tread width.
| Part of the size | Example | What it means |
|---|
| Section width |
205 |
The width of the tyre in mm, also called the tyre tread width. |
| Profile (aspect ratio) |
55 |
The measurement of the sidewall as a percentage of the width - 55% of 205 mm (about 113 mm). |
| Construction |
R |
Radial construction is standard for modern car tyres. |
| Rim diameter |
16 |
Wheel diameter the tyre fits, in inches. |
| Load index |
91 |
Maximum load that the tyre supports. 91 equals 615 kg. |
| Speed rating |
V |
Maximum speed the tyre can handle. V equals 149 mph (240 km/h). |
Type in your tyre size in the decoder above to view this for your car. Then compare the leading brands that match your size and book a fitting nearby.
Your tyre dimensions explained
Car tyre size is expressed in metric format, with each number representing a specific dimension of the tyre. The first number is the section width (or tyre width, or tread width), measured in mm, which is the distance across the tread. The second number, the profile/aspect ratio, sets the sidewall height as a percentage of the tyre width. A greater height percentage is more comfortable, while a lower percentage provides sharper handling.
The letter R indicates radial, and the last number is the rim diameter, measured in inches, which is the size of the wheel that the tyre fits. This tyre calculator then works out the overall diameter, rolling circumference and the number of revolutions per mile.
For passenger vehicles and light trucks alike, these tyre specs dictate the tyre's proper fitting on the wheel, speedometer reading accuracy and the vehicle's driving characteristics.
Most popular tyre sizes in the UK
Jump straight to some of the most-searched tyre sizes:
Plus sizing and changing tyre sizes
When you want to install bigger alloy wheels or consider different tyre sizes, plus sizing allows you to adjust tyre sizes and wheel sizes upwards, while keeping the tyre diameter approximately the same as the original. With our service, you can do a tyre size comparison to check that the new tyre size and the old tyre size fit, as long as the variance in diameter is within a safe range of approximately 3%.
When diameters vary by more than approximately 3%, the speedometer and odometer will start to read incorrectly. With an increased overall diameter, you will have a speedometer reading that shows one speed, however you are going much faster than the reading. Conversely, with a decreased diameter, you will be going slower than the reading. Our tyre size comparison calculator shows you what the new size will be and the speedometer error that will correspond to the new size, giving you the correct speed before you buy.
FAQs about tyre sizes
What does my tyre size signify?
You can find your tyre size by looking for the combination of digits and letters on a tyre's sidewall - for instance, 205/55 R16 91V. From left to right, this shows the section width in mm, the aspect ratio (profile), the construction type, the diameter of the rim in inches, the load index and the speed rating. These factors collectively determine the appropriate tyres for your car.
What is the tyre profile/aspect ratio?
The aspect ratio is the height of the sidewall as a percentage of the tyre's width. In a 205/55 tyre, the sidewall is 55% of 205 mm - approximately 113 mm. A tyre with a lower profile improves handling, while a tyre with a higher profile results in a more comfortable ride.
What does the tyre load index signify?
The load index signifies the maximum weight a tyre can support when the tyre is inflated to its maximum pressure. The load index is assigned a number. For example, index 91 equals 615 kg per tyre. It is important to ensure the tyres fitted to your vehicle meet or exceed its load index requirement.
What does the tyre speed rating mean?
The speed rating signifies the maximum speed a tyre is approved to be driven at. The ratings are associated with letters. For example, V is rated to 149 mph (240 km/h), W to 168 mph (270 km/h) and Y to 186 mph (300 km/h). Your vehicle's speed rating should always be matched or exceeded.
Can I go for a different tyre size?
Sometimes a different tyre size can be used, but the overall rolling diameter should stay within about 3% of the diameter of the original. This will keep your speedometer correct and avoid any rubbing of the tyres. When in doubt, go with the original size specified by the vehicle manufacturer.
Where can I see my tyre size?
Every tyre has the size printed on the outer sidewall. You can also find the recommended sizes on a sticker in the driver's door shut, the inner flap of the fuel filler, or in the vehicle handbook.
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