Tyre Talk - What Do the Numbers Mean?
Each vehicle is equipped with tyres designed to carry a maximum specifed load when operating at a maximum given speed. On the tyre’s sidewall there are various markings, which indicate the tyre’s dimensions and how it may be operated.
Principle markings are:
1. Brand name
2. Model name
3. Section width (mm)
4. Aspect ratio
5. Radial construction
6. Rim diameter
7. Service description - Load & Speed ratings
Tyre Size Markings
Section Width: The tyre’s section width is measured on an ideal width of wheel, for which it has been designed to operate. The measurement distance in millimeters is from the maximum width of the tyre’s mid point of its sidewall to the same point on the opposite sidewall.
Aspect Ratio: This is the height of the tyre’s sidewall expressed as a percentage of the tyre’s section width. In the example, the height of the tyre’s sidewall is 40% of the tyre’s section width or 245 x 40% = 98mm.
Construction Code: R indicates the tyre is manufactured with a radial ply construction.
Rim Diameter: The tyre’s rim diameter is measured in inches taken from the wheel flange where the tyre is seated (bead seat area) to the same point on the opposite side.
Load Index: The load rating, load index or load carrying capacity is represented by a numerical code and is associated with the maximum load that the tyre can carry when operating at its maximum speed rating up to but not exceeding 210kph.
Click here for more details
Speed Index: The speed rating or speed index is represented by a letter and associated with the tyre’s maximum speed capability when operating at its maximum load carrying capacity. A tyre marked with a ‘Y’ speed rating, indicates it can be safely operated at a maximum speed of 300kph. Click here for more details
Other Tyre Marking examples: