Tire information

Information on tire aspect ratio is now included in the sidewall marking, together with the type of construction, and the speed rating.

The speed rating of the tire is given by the letter code, which indicates maximum recommended speed for that tire. Common symbols for passenger car tires include,

• S, for up to 180 kilometers per hour.
• H, up to 210 kilometers per hour.
• V, up to 240 kilometers per hour.
• and Z for over 240 kilometers per hour.

Radial ply tires have always been marked with the section width in millimeters, but with the rim diameter in inches. For example:

• 185 is section width in millimeters.
• 70 indicates a 70% aspect ratio.
• H is the speed rating, for up to 210kilometres per hour.
• R indicates radial ply construction.
• 13 indicates the tire is suitable for fitting to a 13-inch diameter rim.

Totally metric types are also manufactured. For example:

• 190 is the section width in millimeters.
• The aspect ratio is 65%.
• The speed rating is H, for up to 210 kilometers per hour.
• R indicates radial ply construction.
• 390 indicates the tire is suitable for fitting to a 390 mm diameter rim.

Metric-diameter rims cannot be fitted with inch-diameter tires, or vice-versa.

Although tire markings may remain traditional, say, 255,45, Z-R 17, there is a worldwide move towards an I-S-O metric standard which uses letters:

• P for passenger
• LT for light truck
• C for commercial
• and T means temporary use as a spare wheel.

The tire may have a load index number, indicating the maximum load a tire can carry at the speed indicated by its speed symbol, which follows the number.

So a P-series metric size code may read in full - P205-slash-65, R15, 92H.

• P for passenger car tire.
• 205 is the section width in millimeters.
• with 65% aspect ratio.
• R - radial ply construction.
• 15 inch diameter rim.
• 92 load index, for a maximum load of 630 kilograms,
• and H for a speed rating up to 210 kilometers per hour.

Further development of high-speed tires has expanded the speed categories to include W, and Y.

In another example:

• Z indicates a speed over 240 kilometers per hour, but the load and speed rating is taken as the maximum load and speed, that is,
• 89 for a maximum load of 580 kilograms,
• and W for 270 kilometers per hour.