All-season tires: 205/55 R16

The width of your tyre, in millimetres, measured from sidewall to sidewall.

This is the ratio of the tyre’s cross-section to its width, expressed as a percentage. An aspect ratio of 65, for example, indicates that the tyre’s height is 65% of its width.

The diameter (height) of the wheel in inches.

Your tyre’s load index relates to its maximum carrying capacity (in kg). You’ll find the load rating of your tyre on the sidewall, just to the right of the diameter.

For example, a tyre with a load index of 91 can carry 615kg of weight.

Load ratings and speed ratings should be looked at together when you buy a new tyre. Also remember to check your manufacturer’s recommendations.

The speed rating is the maximum speed for a tyre when it is correctly inflated and being used under load. The speed rating is the letter at the end of the sidewall, after the load index number. A tyre with a speed rating of V, for example, has a maximum speed of 240 km/h.