Let's say the large set of numbers on the sidewall of a tyre reads 215/45 R17 84V.

 

215- This is the width of the tyre across its tread in millimetres. If you took a ruler and measured the tread, it would read about 21.5cm, or 215mm.

 

 

45 - This is the width of the sidewall, as a percentage of the width of the tread. This tyre's sidewall is 45 percent of the tread. If you measured it with a ruler, it would be just under 10cm. An off-road tyre or a tyre designed for comfort will usually have a higher profile number. A performance tyre, also known as a 'low profile' tyre, will have a smaller profile.

 

 

R17 - The R stands for radial; this is a radial road tyre. The 17 is the diameter of the wheel or rim in inches, therefore this tyre is designed for a 17-inch rim. Want to check what size your rim is? The size is typically stamped inside the rim on one of the spokes, or you can measure across the spokes from one inside edge to the other.

 

91W - this is the load index and speed rating of the tyre. Essentially, the load rating, represented by the numerical value, is related to the maximum weight that tyre can carry. The tyres load index must meet or exceed the value displayed on the vehicle's tyre placard. The speed category symbol, represented by the alphabetical value, indicates the maximum speed at which the tyre can carry a load corresponding to its load index.