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How To Find Your Tyre Size

If you’re in need of new tyres then the first thing you’ll need to know is what tyre size your vehicle needs.

You can start searching for your tyre size by inputting your registration number, however for many vehicles there may be more than one size option and so to narrow your search you’ll need to look for the information on the vehicle itself.

Here’s our handy guide to understanding & reading your tyres.

Where to find your tyre size

The best place to find your tyre size is on the sidewall of the tyres currently fitted to your car. Some vehicles such as BMW’s & Mercedes have different sized tyres on the front and rear so if you check on the tyre you need replacing you can be sure you’re replacing your tyre with one exactly the same size. Reading the markings on your tyres may look confusing, however once you know what to look for finding your tyre size is actually fairly easy.  

Tyre size information can also be found:

• In your vehicle handbook
• Inside the fuel flap
• Inside your glove box
• Inside the driver’s door panel

Top Tip: If you have a smart phone then take a quick photograph of the numbers on the side wall of your tyre. This way you’ll always have your tyre size to hand – when you’ve learnt how to crack the code!

How to read your tyre size

225mm tyre width

Tyre Width

225/40R18 92Y

The first 3 digits of the tyre size give the measurement for the width of the tyre in mm. So a 205 width tyre will measure exactly 205mm across the tread from one sidewall to the other.

arrow showing width of tyre
Tyre profile of 40

Tyre Profile

225/40R18 92Y

The next pair of numbers give the measurement for the height of the tyre as a percentage of the tyre width. In this case, the aspect ratio is 40 which means that the height of the tyre is 40% of the tyre width.

The profile is 40% of tyre width
Tyre radial construction

Tyre construction

225/40R18 92Y

The next marking is a letter, in this case the letter “R”.

R stands for Radial which means the tyre has a radial construction. The vast majority of modern tyres are made with a radial construction.

tyre construction
Tyre wheel or rim size in inches

Tyre diameter

225/40R18 92Y

The last 2 numbers found after the ‘R’ show the size of the wheel rim on the vehicle. In this case, the tyre marked with ‘16’ tells us that the wheel it fits on to is 16” in diameter.

Load & Speed rating

225/40R18 92Y

The load & speed rating are the last elements you need to know.

The load rating tells you the maximum weight capacity of a passenger car tyre.

The speed rating is shown as the letter at the very end of the tyre size. The higher the letter alphabetically, the higher the speed rating for your vehicle. You can fit a tyre with a higher speed rating than necessary but never a lower rating than required.

If you need further advice on tyre sizes then don’t hesitate to contact your local branch or call our team on 0345 2997 955