Why Do Tire Widths End in ODs?

The width of a car tire is always denoted by a number ending in 5, and this is no mere coincidence. This peculiarity stems from technical regulations set forth by the European Tyre and Rim Technical Organization (ETRTO) and the ISO 5775 standard.

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The ETRTO, established in 1964, is responsible for setting tire size standards for the European market. A key regulation by the ETRTO is that tires for passenger cars, light trucks, and commercial vehicles must have a width ending in a 5 to differentiate them from motorcycle and agricultural vehicle tires.

This is important for standardization in the tire industry. Having car tire widths end in 5 makes it easier for manufacturers, distributors, and consumers to identify, produce, and choose the right tires for their vehicles.

It ensures consistency in production and that products meet certain safety and performance standards. Standardization also simplifies tire design and installation, ensuring a proper fit and optimal performance for vehicles manufactured to these standards.

*As illustrated below, car tire widths always end in 5.*

Typically, tire size specifications are printed on the tire sidewall, for example, 205/45R17 or 225/60R16. Here, the first number, 205 or 225, indicates the tire width in mm, ranging from 155-315mm depending on the vehicle type.

The next two numbers after the slash denote the tire’s aspect ratio, which is the percentage of the tire’s sidewall height to its width, typically between 55-75% for most passenger cars.

The letter ‘R’ indicates the radial construction of the tire, an industry standard for passenger cars, and the most common type of tire. Other types may be denoted by B, D, or E.

Finally, the last number in the sequence, such as 17 or 16, represents the wheel diameter in inches that the tire is designed to fit.

These are the basic parameters that car owners need to consider when choosing tires that match the size specifications provided by the vehicle manufacturer.

*Source: VTC news*

Frequently asked questions

Tire widths are commonly measured in millimeters or inches, but the measurements are often followed by an ‘OD’, which stands for ‘Outer Diameter’. This refers to the overall diameter of the tire, including the wheel and the tire itself. The OD is an important factor in ensuring the tire fits the vehicle’s specifications, as it affects the vehicle’s speedometer and odometer readings, as well as its handling and performance.

The outer diameter of a tire impacts its performance in several ways. Firstly, it affects the vehicle’s speedometer and odometer readings – a larger OD will cause the readings to be higher than actual, and vice versa. Secondly, the OD influences the tire’s contact patch, which is the area of the tire that is in direct contact with the road. A larger OD can provide a larger contact patch, improving traction and handling, especially in wet or slippery conditions.

Matching the tire’s outer diameter to the vehicle’s specifications is crucial for maintaining optimal performance and safety. If the OD is not correct, it can affect the accuracy of the vehicle’s speedometer and odometer, which can impact fuel efficiency and maintenance intervals. Additionally, an incorrect OD can affect the vehicle’s handling and ride quality, potentially compromising safety and driving comfort.
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