Why does the width of a car tire end with the number 5?

ETRTO was established in 1964 and is responsible for setting the standard tire model for sale in Europe. According to ETRTO regulations, tires for passenger cars, light trucks and commercial vehicles must have a tire width ending in the number 5 to avoid confusion with tires for motorcycles and agricultural vehicles.

Another important reason is the uniformity and standardization in the tire industry. The fact that the width of a tire ends in the number 5 makes it easier for manufacturers, distributors and consumers to identify, produce and purchase tires suitable for different types of vehicles.

This not only helps increase consistency in the manufacturing process, but also ensures that products meet certain safety and performance standards.

Additionally, specifying tire widths ending in the number 5 also simplifies tire design and installation, ensuring that tires will fit and perform effectively on vehicles built to this standard.

Normally, on the surface of the tire sidewall, tire size parameters are printed with indexes, for example: 205/45R17 or 225/60R16...

In which, the index 205 or 225 is understood as the tire width. Depending on each type of vehicle, this index will fluctuate between 155 - 315 and is calculated in mm.

The next two numbers after the slash are the tire profile, which is the percentage of the tire sidewall height compared to the tire tread width and is usually between 55 - 75% for most passenger cars.

R stands for Radial construction, an industry standard for passenger cars and the most common tire type. Other vehicle types may be B, D or E.

The last number in the character range, such as 17 or 16, indicates the diameter of the rim that the tire fits, in inches.

These are basic indicators for car users to choose the right tire size for the car that has been equipped by the manufacturer right from the factory.

Pham Duy (synthesis)