Width: The width of the tyre in millimetres, in our example this is 235.
Profile: The height of the tyre sidewalls as a percentage of the width is 55.
Radial: This means the type of tyre, in our example it’s R. Other letters you may see are ZR, indicating that the tyre is for high speeds or RF which indicates that it is a run flat tyre.
Diameter: 17 is the diameter of the tyre’s inner rim. It is always expressed in inches. The number varies between 10 and 23 inches for passenger vehicles.
Load Index: This is an index of the maximum load carrying capacity per tyre at the speed designated by the speed symbol, 99 in this case.
Speed Index: The last letter indicates the maximum speed for the tyre at full load. W corresponds to a maximum speed of 270 km/h. This should generally be higher than your vehicles maximum speed, however, there are exceptions for winter tyres and exemptions in some countries.
Width = 235mm
Profile = 55%
Radial = type R tyre
Diameter = 17inches
Load Index = 99
Speed Index = W