Reading the sidewall of a tire

The sidewalls contain a lot of information that will come in handy when you have to purchase tires. The code indicates, from left to right, the type of tire, section width, sidewall aspect ratio, tire construction, diameter, load index, and speed rating.

P225/55R18 97T

Type of tire (“P” in the example above): This letter tells you the type of vehicle that the tire was designed for. For example, “P” designates a passenger car, SUV, or pickup truck; “LT” means a work truck; “T” signifies a spare tire; and “ST” means a trailer. If there isn’t a letter, it indicates that it is a European metric tire.

Section width (“225” in the example above): This number indicates the distance (in millimetres) between the sidewalls.

Sidewall aspect ratio (“55” in the example above): This number is the sidewall width as a percentage and indicates the height between the wheel and the road. The lower the number, the thinner the tire (for instance, a performance car); the higher the number, the thicker the tire (for instance, a 4×4).

Tire construction (“R” in the example above): This letter refers to the construction of the tire interior. “R,” which represents 99% of all tires, stands for “radial.” This means that the plies of the tire body cross the tire from one bead to another. “D” and “B” are used for specialized equipment.

Wheel diameter (“18” in the example above): This number indicates the diameter of the wheel in inches.

Load index (“97” in the example above): This is the maximum load a tire can support when inflated to the maximum safe pressure. In the example above, “97” corresponds to a maximum capacity of 730 kg.

Speed rating (“T” in the example above): This number indicates the maximum guaranteed speed that the tire can handle. Speed ratings range from A (lowest) to Y (highest). For instance, the popular “H” rating can handle sustained speeds of 210 km/h!

And don’t forget that, in the winter in Quebec, you must have tires with the mountain and snowflake symbol.

Now you know everything you need to know to understand the code on your tires!