Read the sidewalls of your current tyres. On most tyres, the size information is right on the tyres. An example of this information: “P 185/75 R14 82S.” The P stands for “passenger tyres,” 185 indicates the width in millimetres. 75 refers to the height of the tyre divided by the width (also known as the aspect ratio). R indicates the radial construction. 14 refers to the diameter of the full tyre in inches. 82 indicates the load rating, and S indicates the speed rating. Load rating is the amount of weight your tyres can support. The number on the tyre corresponds to a specific weight. For example, an 82 load rating indicates that the tyre can support a load of 475 kilograms. The speed rating indicates how well the tyre handles at top speeds. For example, S indicates that the tyre can handle well up to 180 km/h.