With a little explanation it's easy to understand what all of the letters and numbers mean on your tire's sidewall. The numbers are indicators of the size, type, and performance of the tire.
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The letter "P" at the beginning of the "Tire Size" tells us the tire is a P-Metric tire, referring to tires made to certain standards within the United States, intended for Passenger vehicles.
If a tire size has no letters at the beginning, this indicates a Euro metric tire. P-Metric and Euro-Metric tires may have different load capacities.
The letters "LT," either at the beginning or at the end of the tire size indicate the tire was designed for light trucks. Vehicle manufacturers equip some light trucks with "LT" type tires. These tires generally require higher inflation pressures than passenger tires.
Consult your owner's manual or tire placard for the recommended tire size and inflation pressure for your vehicle.
Tire Width
Is the width of the tire measured in millimeters from sidewall to sidewall. The first three-digit number in the tire size refers to the tire width. For instance, in a size P215/65 R15 tire, the width is 215 millimeters.
Aspect Ratio
Is the ratio of the height of the tire's cross-section to its width. The two-digit number after the slash mark in a tire size is the aspect ratio. For example, in a size P215/65 R15 tire, the 65 means that the height is equal to 65% of the tire's width. The bigger the aspect ratio, the bigger the tire's sidewall will be.
The letter "R" in a tire size stands for Radial, which means the layers run radially across the tire.
Wheel Diameter
Is the size of the wheel measured from one end to the other. It tells us the size of the wheel that the tire is intended to fit. A size P215/65 R15 tire is made for a wheel with a 15" diameter.
Load Index
Indicates the maximum load that the tire can support when properly inflated. You'll also find the maximum load on the tire sidewall, in both pounds and kilograms. Learn more abouttire load index.
Speed Rating
Tells you the maximum speed capability of a tire. Often speed ratings are matched to the top speed capability of the vehicle. For example, a tire with an H-speed rating has a maximum speed capability of 130 mph or 210 km/h. Goodyear does NOT recommend exceeding legally posted speed limits. Learn more abouttire speed rating.
DOT Symbol
The letters "DOT" on the sidewall indicate that the tire complies with all applicable Federal Motor Vehicle Safety Standards in the United States.
Tire Identification Number
The series of letters and numbers following the letters "DOT." The TIN consists of up to 12 numbers and letters to identify the factory location and the week and year the tire was manufactured.
UTQG
Stands for Uniform Tire Quality Grading, a rating system developed by the U.S. Department of Transportation to provide consumers with information to help them purchase tires based on their relative treadwear, traction and temperature capabilities.
Traction grades indicate the wet traction of a tire under a controlled test. A tire with an "AA" rating offers outstanding traction in wet conditions.
Traction Grades
AA
A
B
C
Temperature grades indicate the ability of the tire to withstand and dissipate destructive heat. A tire with a higher temperature grade is able to operate at higher speeds.
Temperature Grades
Speeds in mph
A
Over 115
B
Between 100 and 115
C
Between 85 and 100
Treadwear grades are based on standardized government tests to help predict the expected treadwear of a tire. For example, a tire with a treadwear grade of 200 should last twice as long as a tire with a treadwear grade of 100.
Automotive tires are described by an alphanumeric tire code (in North American English) or tyre code (in Commonwealth English), which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of its key limitations, such as load-bearing ability, and maximum speed.
(a series of letters and numbers) on your tire's sidewall. The first 3-digit number tells you the tire width in millimeters. The next 2-digit number is the aspect ratio of the tire section's height and width. The following 2-digit number displays the tire's rim diameter in inches.
The number 215 indicates the tire width in millimeters from sidewall to sidewall, so 215 millimeters in this case. 65 is the aspect ratio code, which means the ratio of its height to width. This tire has a height equal to 65% of its width. R indicates radial construction.
Tire width is represented by the three numbers following the tire type letter. The numbers are the width of the tire in millimeters measured from sidewall to sidewall. In our example of P215/65 R15 95H, “215” means this tire is 215 millimeters wide from sidewall to sidewall.
Once you choose a tire size for your vehicle, you'll want to stick with that size when you buy replacements. The reason for this is that a differently sized tire can confuse your speedometer and even cause damage to your vehicle's anti-lock braking systems and stability system calibrations.
One way to determine the rim size for your vehicle is to look at the alphanumeric tire size code located in the owner's manual, driver's side door jamb, or inside the glove box door. Look for a code like P215/65 R15 95H.
The first series of three numbers tells you the width of the tire tread in millimeters. Width tread may range from 155 to 315. The two numbers after the slash show the aspect ratio of the tire. This is the tread-width percentage that is equal to the sidewall's height.
225/50R18 tires have a diameter of 26.9" (683 mm), a tread width of 8.9" (225 mm), and a wheel diameter of 18" (457.2 mm). The sidewall of the tire is 4.4" (113 mm), and the tire's circumference is 84.5" (2144.6 mm). This means a 225/50R18 tire will make make 750 revolutions per mile, or 466 revolutions per kilometer.
Tire width is represented by the three numbers following the tire type letter. The numbers are the width of the tire in millimeters measured from sidewall to sidewall. In our example of P215/65 R15 95H, “215” means this tire is 215 millimeters wide from sidewall to sidewall.
The first number in the tire size, 275, represents the width of the tire in millimeters. To convert this to inches, we divide 275 by 25.4 (since there are 25.4 millimeters in an inch). This gives us approximately 10.8 inches.
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