Tires and wheels with unique rim diameters should never be combined with traditional 'inch rim' tires and wheels. These are the most common types of tire sizes and are used on most cars, minivans, vans, sport utility vehicles and light duty light trucks. The 17 indicates the tire and wheel diameter designed to be matched together. Tires using this construction are for light truck and spare tire applications. If the R in the size was replaced with a D ( P225/65R17 100T), it would identify that the internal tire body plies crisscross on a diagonal and that the tire has a 'bias ply' construction. Radial tires are by far the most popular type of tire today representing over 98% of all tires sold. The R in the P225/65R17 100T size identifies that the tire has a radial construction in which the tire's plies 'radiate' out from the center of the wheel. By converting the 225mm to inches (225 / 25.4 = 8.86') and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43'. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm.

The lower the number, the lower the sidewall. The higher the number, the taller the sidewall. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The 65 indicates that this tire size's sidewall height (from rim to tread) is 50% of its width. Typically, following the three digits identifying the tire's width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio. 65 means that the height is equal to 65% of the tire's width. The ratio of the height of the tire's cross-section to it's width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the width in millimeters by 25.4 (the number of millimeters per inch). The 225 indicates that this tire is 225 millimeters across from the widest point when mounted and measured on a specified width wheel. The use of p-metric sizes began in the late 1970s and they are the most frequently used type of tire size today.įollowing the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's section width/cross section in millimeters. This includes cars, minivans, sport utility vehicles and light duty pickup trucks (typically 1/4- and 1/2-ton load capacity).

When a tire size begins with a P, it signifies the tire is a p-metric size that was designed to be fitted on vehicles that are primarily used as passenger vehicles.

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