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Tire Sizing

Passenger Tire Sizing

P-Metric

Passenger & Light Truck Tire Sizing - Passenger Tire Sizing

Today, most U.S. tire manufacturers build tires that conform to this system. It evolved in the late seventies in an attempt to standardize tire sizing worldwide and is based on the metric system.

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 (Load Index and Speed Rating)

Light Truck Metric

This sizing system mirrors the P-Metric system for passenger tires.

LT235/75R15/C
LT = Light Truck Designation
235 = Section Width in Millimeters
75 = Aspect Ratio
R = Radial Construction
15 = Rim Diameter in Inches
C = Load Range

Alpha-Numeric

In the late sixties, this load-based system evolved. The first letter of the designation identifies the load/size relationship of the tire. The letter can range from "A" to "N", with "A" being the lowest. The lower the letter, the smaller the size and load-carrying capacity at a given air pressure.

BR60-13
B = Load-Carrying Capacity
R = Radial Construction
60 = Aspect Ratio
13 = Rim Diameter in Inches

Millimetric

240/55R390
240 = Section Width in Millimeters
55 = Aspect Ratio
R = Radial Construction
390 = Rim Diameter in Millimeters

European Metric

Essentially this system was a conversion of the Numeric system from inches to millimeters. Aspect ratio appears in the size designation in most cases where it is other than 82.

155SR13, 155R13, 155R13 78S 155 = Section Width in Millimeters
S = Speed Rating (See pages 7&8)
R = Radial Construction
13 = Rim Diameter in Inches
78S = Service Description (Load Index and Speed Rating)