Sizing Systems: Passenger Tire Sizing

Four sizing systems exist for passenger tires today, but we'll explain the two most commonly used:

P-Metric

Examples: P215/65SR15, P215/65R15, P215/65R15 95S
P = Passenger Car Tire
215 = Section Width in Millimeters
65 = Aspect Ratio
R = Radial Construction
15 = Rim Diameter in Inches
95S = Service Description

European Metric

The aspect ratio is assumed to be 82 if not present in identification number.

Examples: 155SR13, 155R13, 155R13 78S
155 = Section Width in Millimeters
S = Speed Rating
R = Radial Construction
13 = Rim Diameter in Inches
78S = Service Description

Examples: 185/70SR14, 185/70R14, 185/70R14 88S
185 = Section Width in Millimeters
70 = Aspect Ratio
S = Speed Rating
R = Radial Construction
14 = Rim Diameter in Inches
88S = Service Description