Tire Sidewall Markings: Every Number and Symbol Decoded

Where the markings live

The sidewall is the part of the tire between the tread and the bead. Standard No. 139, the Federal Motor Vehicle Safety Standard for new pneumatic radial tires for light vehicles, defines a sidewall as the portion of a tire between the tread and the bead. The bead is the steel-wire bundle shaped to fit the rim, so the sidewall is the tall rubber band you can read without jacking the car.

Most markings are molded into the rubber and are meant to survive the life of the tire. Because sidewalls flex, some letters and numbers appear on both sides, and a few labels are required on at least one sidewall. Read the tire while it is mounted on the vehicle, note the markings that matter for replacement, and bring that information with you when you shop.

• Size code: identifies the tire's dimensions and intended fitment.
• Service description: states the load index and speed symbol.
• DOT identification: the symbol required for tire identification and recordkeeping.
• Construction and load range: shows whether the tire is radial or bias ply and how much load it carries.
• UTQG grades: comparative treadwear, traction, and temperature resistance ratings.
• Snow symbol: marks a tire designed for severe snow service.
• Maximum load and pressure: the limits molded into the sidewall.

The size code

The first group of characters on the sidewall is the tire size designation. Federal rules for retreaded passenger tires require the casing to keep the tire size permanently molded on the sidewall, and new tires must be designed to fit the rims listed for their size. When you are comparing replacements, this code is the first thing to check.

The size code packages several measurements in a single series: section width, aspect ratio, construction, and rim diameter. Section width is measured between the exteriors of the sidewalls of an inflated tire, and rim diameter is the nominal diameter of the bead seat. The way those values are presented in the code is explained in tire size explained.

Load and speed: the service description

After the size code, look for the service description: a load index paired with a speed symbol. The standards define load rating as the maximum load a tire is rated to carry for a given inflation pressure. Under Standard No. 110, the vehicle maximum load on a passenger car tire must not exceed the applicable maximum load rating marked on the sidewall. The same standard says the vehicle normal load on the tire must not be greater than 94 percent of the load rating at the vehicle manufacturer's recommended cold inflation pressure.

The speed symbol is a letter that describes the tire's rated speed capability. Together, the load index and speed symbol tell you whether the replacement tire can handle the same loads as the original. For a full explanation, read tire service description and tire speed rating guide.

Light truck tires use a separate load range system; the distinction is covered in what is tire load range.

Construction and load range

The sidewall also tells you how the tire is built. A radial ply tire has ply cords that extend to the beads at substantially 90 degrees to the centerline of the tread. A bias ply tire lays those cords at alternate angles substantially less than 90 degrees. The construction letter is one part of the size code, and the broader differences are covered in tire construction types.

Some tires are built to handle more load. Standard No. 139 defines an extra load tire and a reinforced tire as tires designed to operate at higher loads and higher inflation pressures than the corresponding standard tire. If your replacement needs that capability, look for the extra load or reinforced marking and compare extra load tires XL.

DOT code and date

The symbol DOT is the tire identification required by 49 CFR Part 574. It marks a new tire as certified and gives the identification code used for recordkeeping. Retreaded tires also must carry the symbol DOT, and the retread standard requires the size and the actual number of plies or ply rating to remain permanently molded on the casing. For reading the date portion of the code, see tire DOT date code.

UTQG grades

Many passenger tires carry the Uniform Tire Quality Grading labels required by 49 CFR 575.104. The sidewall shows three grades: treadwear, traction, and temperature resistance. Traction grades are AA, A, B, or C, and temperature grades are A, B, or C. Treadwear is a comparative number rather than a fixed mileage promise.

The grading rule does not apply to every passenger tire. It excludes deep tread winter-type snow tires, space-saver or temporary spares, tires with nominal rim diameters of 12 inches or less, and limited production tires. For more on how to read the grades, see treadwear rating explained and traction temperature rating.

Snow, pressure, and TPMS labels

Severe snow tires carry a dedicated symbol. Standard No. 139 defines a snow tire as one that attains a traction index equal to or greater than 112 in the specified snow traction test and is marked with the Alpine Symbol on at least one sidewall. That symbol is the three-peak mountain with a snowflake. For more, see snow tire symbol guide.

The maximum pressure molded on the sidewall is not the pressure to use. The U.S. Department of Energy's fuel economy guide says the proper tire pressure for your vehicle is usually found on a sticker in the driver's side door jamb or the glove box and in your owner's manual, and it warns not to use the maximum pressure printed on the tire's sidewall. Keeping tires inflated to that placard pressure also helps fuel economy: properly inflated tires can improve gas mileage by 0.6 percent on average, up to 3 percent in some cases, and under-inflated tires can lower gas mileage by about 0.2 percent for every 1 psi drop in the average pressure of all tires.

If pressure drops too far, the vehicle's tire pressure monitoring system should alert you. Under Standard No. 138, the system must illuminate a low tire pressure warning telltale no more than 20 minutes after the pressure in one or more tires is equal to or less than the pressure 25 percent below the vehicle manufacturer's recommended cold inflation pressure, or the pressure specified in the standard, whichever is higher. See tire pressure basics and do I need tire pressure monitoring system.

What to look for when you shop by sidewall marking

Questions

What does every marking on a tire sidewall mean?

The main markings are the size code, the service description with its load index and speed symbol, the DOT identification, construction and load range, UTQG grades, the snow symbol, and the maximum load and inflation pressure. Start by matching the size code and service description to your vehicle's requirements.

Where is the date code on a tire?

The date is part of the DOT identification required by 49 CFR Part 574. The exact format and how to read it are covered in the DOT code and date section above.

Should I inflate tires to the maximum pressure on the sidewall?

No. The U.S. Department of Energy's fuel economy guide says the proper pressure is found on the vehicle placard and in the owner's manual, not the maximum pressure printed on the sidewall.

What is the service description on a tire?

It combines a load index and a speed symbol to describe the tire's rated load and speed capability. It appears near the size code and should be matched when you replace a tire.

Do all tires have UTQG grades?

No. 49 CFR 575.104 applies to passenger car tires but excludes deep tread winter-type snow tires, space-saver or temporary spares, tires with nominal rim diameters of 12 inches or less, and limited production tires.

What does the Alpine symbol mean?

Standard No. 139 defines a snow tire as one that reaches a traction index of at least 112 in the required snow traction test and is marked with the Alpine Symbol on at least one sidewall. Knowing this helps you identify severe snow service tires.