Your tyre size is always written as a sequence of numbers and letters on the tyre sidewall. In the example below we will use a tyre size 185/55 R15 81H – which can split into 5 parts:
Width (185) – the width of your tyre in millimetres
Profile (55)- This is the size between wheel rim and the top of the tyre, measured as a percentage of the tyre width
Tyre size (R15) – This is the diameter of the rim in inches
Load index (81) – this refers to the load capacity in kilograms of the tyre. This number is an index, with the number referring to a KG load.
Speed index (H) – this refers to the maximum speed the tyre can be safely driven at. This letter is an index, with the letter referring to a KPH speed.
For more information on reading the information on your tyre watch this video click here.