What unit is used for tires?
2 Answers
Tires are measured in millimeters. Their international standard codes represent the section width and aspect ratio percentage, followed by the tire type code, rim diameter in inches, load index indicated by load-carrying capacity codes, and permissible speed codes. Tires are circular elastic rubber products assembled on various vehicles or machinery to roll on the ground. Mounted on metal rims, they support the vehicle body, cushion external impacts, ensure contact with the road surface, and maintain driving performance. The functions of tires are: 1. Directly contacting the road surface and working with the vehicle suspension to mitigate impacts during driving; 2. Ensuring good ride comfort and smooth driving; 3. Maintaining excellent adhesion between the wheels and the road surface; 4. Improving the vehicle's traction, braking, and off-road capability; 5. Bearing the weight of the vehicle.
I've been repairing cars for over a decade and often get asked about tire units. Tire sizing is a classic example of mixed units. Take the 205/55R16 marking for instance: 205 indicates the section width in millimeters; 55 is the aspect ratio, representing the percentage of section height to width; R stands for radial construction; and the final 16 is the rim diameter in inches. These unit parameters must be strictly matched when replacing tires. Last week, a customer measured inch rim sizes using centimeters and ended up buying the wrong size. Also note that tire pressure units are divided into bar and psi, with standard passenger car tires typically between 2.2-2.5 bar. Always refer to the original vehicle manual or sidewall markings for units - mixing measurement systems can directly impact driving safety.
