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Tire Sizing System
There are a number of different systems in use today that describe the various tire sizes used on performance, passenger and light truck vehicles. An attempt is currently underway to develop a worldwide system, but presently you must be familiar with several different systems.
- Custom or Alloy Wheels
While custom or alloy wheels require an increased level of care over steel wheels, it is vitally important that each customer receives the highest level of service. There are several key points to note when mounting Yokohama tires. Following these basic precautions yields consistent results.
- Alpha-Numeric Sizing System
In 1968, a new concept was introduced worldwide. The Alpha-Numeric sizing system is a load-based system where tires are designated by their load-carrying capacity and aspect ratio. The first letter is the load and size relationship, with letters ranging from A to N. The lower the letter, the smaller the size and, of course, the lower the load-carrying capacity of the tire.
- P-Metric Sizing System
To accommodate the smaller tires used on compact cars, the P-Metric (Passenger Metric) system was created in 1976. The maximum inflation pressures of P-Metric tires were raised for lower rolling resistance. The P-Metric system is widely used by domestic tire manufacturers.
- Metric Sizing System
Because Europe primarily uses the metric system of measurement, the metric sizing system was developed. It is essentially a conversion of the Numeric system. Section widths are notated in millimeters instead of inches. Originally, tires not identified with an aspect ratio were assumed to be 82-series. When 60- and 70 series tires appeared, the aspect ratio was added to the nomenclature, similar to the P-Metric system.
- ISO Metric Sizing System
International Standards Organization (ISO) Metric system combines the Metric system with a service description. The service description provides the load index along with the speed rating symbol.
- Millimetric Sizing System
The Millimetric sizing system is similar to the Metric system except that the rim diameter is also represented in millimeters. These rim diameters are unique in size and can only be used in combination with each other.
- Light Truck Numeric System
Similar to the Numeric system for cars, it lists the section width in inches, construction type, rim diameter in inches, plus the light truck designation.
- Light Truck Metric Sizing System
Similar to the P-Metric system, except the P is replaced with the LT light truck designation. Also, LT-Metric and P-Metric tires differ in construction.
- Light Truck High Flotation System
The same as the Light Truck Numeric system with tire diameter added to the front.
These rim diameters are unique in size and can only be used in combination with each other.
I explain the metric sizing system and some other very important tire info
The sidewall of your tires is filled with important information that tells you everything you need to know about your tire. The numbers can be a bit overwhelming to the untrained eye, so the best way to understand tire markings is to take an example and break it down, bit...