Steps to Calculate your tyre size
Learn to calculate your tyre size by understanding what the sidewall markings on your tyres stand for. Knowing the correct tyre size for your vehicle is crucial for optimal performance and safety.
Take the guesswork out of the equation and learn the precise measurements you need with our tyre size calculator. Whether you’re a seasoned driver or a novice, our tyre size calculator article will help you ensure you purchase the right size tyres every time.
While it might look confusing at first, it can be easily worked out. Follow the breakdowns in the table below to properly calculate the size of your tyres.
Sidewall Marking | Explanation |
|---|---|
205 | The width of the tyre in millimetres |
55 | The height of the tyre sidewall as a percentage of the width |
R | The tyre is of radial construction |
16 | The tyre’s inner rim diameter in inches |
91 | The load rating of the tyre |
W | This speed rating – the tyres maximum speed at full load |
Get to know your Tyres
Now you know what each value stands for, it’s time to work out what it all means.
Load Rating
The tyre load rating is usually found between the diameter reading and the speed rating on the sidewall marking.
This rating shows how much a tyre should be able to carry when inflated to its limit. It shouldn’t be mistaken for the weight of the tyre itself.
Why is load rating so important?
Tyres are made to withstand a certain amount of weight. An overloaded tyre has a higher risk of low pressure or blowing out, so it is especially important to refer to this if you are planning to add extra weight to your vehicle.
Your car insurance policy may become void if you have tyres with an incorrect load capacity. It is vital that you check that tyres with correct load ratings are fitted to your car.
Speed Rating
The final letter indicates what speed the tyre can safely reach when fitted to a vehicle. We have broken it down further in this table.
Speed Symbol | Max Speed mph | Max Speed km/h | Speed Symbol | Max Speed mph | Max Speed km/h |
|---|---|---|---|---|---|
M | 81 | 130 | H | 130 | 210 |
P | 93 | 150 | V | 150 | 240 |
Q | 99 | 160 | W | 169 | 270 |
R | 106 | 170 | Y | 187 | 300 |
S | 112 | 180 | ZR | Over 150 | Over 240 |
T | 118 | 190 |
The speed rating is decided from tests carried out by engineers, which involve running the tyre at 6.2mph in 10-minute increments until the required speed has been met.
Why is speed rating so important?
If the tyres fitted to your car have a lower speed rating than they should, your car insurance policy could be invalidated. So, it is important to check this speed rating before buying new tyres.
I’ve calculated my tyre size, now what?
Now that you know how to calculate the size of your tyres, you can use the search to find the perfect tyres to suit your vehicle. All tyres available in your tyre size will be found, showing premium, mid-range and budget brands, each with their own features and technologies to suit the needs of many drivers.