The first three-digit number is the tire width in millimeters measured at its widest part, not the tread. It is also called the section width. High-performance car tires tend to have higher section width than more mainstream vehicles.
The two-digit number following the slash in the tire size description is the tire?s aspect ratio. It is the sidewall height expressed as a percentage of the tire?s width. If the markings say 255/55R18, it means that the height of the sidewall is 255 multiplied by .55, or 140 millimeters.
The higher the aspect ratio, the taller the sidewall is in relation to the tread width. If it is a low number, it means that it is a low-profile tire such as those found on higher-performance cars. The 2018 Chevrolet Camaro ZL1, for example, has 285/30ZR20 tires on its front wheels with sidewalls only 30 percent as tall as the tire is wide.
The next part of the tire size is a letter denoting its construction, sometimes a Z speed rating, and the size of the wheel that it is designed to fit, measured in inches. When it says R18, it means that it has a radial-ply construction and it fits an 18-inch rim.
The two-digit number following the slash in the tire size description is the tire?s aspect ratio. It is the sidewall height expressed as a percentage of the tire?s width. If the markings say 255/55R18, it means that the height of the sidewall is 255 multiplied by .55, or 140 millimeters.
The higher the aspect ratio, the taller the sidewall is in relation to the tread width. If it is a low number, it means that it is a low-profile tire such as those found on higher-performance cars. The 2018 Chevrolet Camaro ZL1, for example, has 285/30ZR20 tires on its front wheels with sidewalls only 30 percent as tall as the tire is wide.
The next part of the tire size is a letter denoting its construction, sometimes a Z speed rating, and the size of the wheel that it is designed to fit, measured in inches. When it says R18, it means that it has a radial-ply construction and it fits an 18-inch rim.
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