315/40R21 - Silverstone Tyres

Your tyre size can be found on the sidewall of your current tyre and is a sequence of numbers and letters. It’s important to check your existing tyre or to check your vehicle handbook to ensure the right tyre size has been installed.

Tyre Width

The first three digits. This displays the width of the tyre in millimetres. A tyre marked 225 will measure 225mm across the tread from sidewall to sidewall.

Aspect Ratio

The fourth and fifth digits of the tyre code that immediately follow the tyre width. The aspect ratio or profile height of the tyre sidewall is expressed as a percentage of the tyre width. So an aspect ratio of 55 for example means that the profile height of the tyre is 55% of its width.

Rim Diameter

The next two digits represent the size of the wheel rim that the tyre can be fitted to. It is also the diameter of the tyre from bead to bead. So a tyre marked 16 will fit on a 16-inch wheel rim.

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