Tire Sidewall Markings: What Every Number Means
John Pearley Huffman draws on years of experience exploring cars and the decisions vehicle owners face. His knowledge covers how vehicles work, what makes them different, and practical considerations for understanding everyday automotive questions.
Quick answer
A tire sidewall shows size, load capacity, speed rating, manufacture date, and quality grades you can decode in under a minute. Read the size code first, such as 235/65R17, to get width, shape, and rim size. Then find the load index and speed letter right after the size code. Look for the four-digit DOT date code to know the tire's age.
The Size Code: Width, Profile, and Rim Diameter
The largest string of characters on the sidewall is the size code, and it tells you three things at once. Take a common example: 235/65R17.
- 235 is the tire’s cross-section width in millimeters, measured at the widest point.
- 65 is the aspect ratio: the sidewall height is 65 percent of the width. A lower number means a shorter, sportier sidewall.
- R means radial-ply construction, which is standard on virtually all modern passenger tires.
- 17 is the wheel rim diameter in inches. This must match your wheel exactly.
Some tires begin with a letter prefix. P stands for passenger vehicle. LT means light truck, a designation that affects load and inflation ratings. If you see no prefix, the tire follows a different (Euro-metric) sizing standard with slightly different load rules.
When replacing tires, Consumer Reports recommends staying with the size and speed rating of your car’s original tires. If you bought a used car, check the owner’s manual or the driver’s door-jamb placard, because a previous owner may have installed the wrong size.
Load Index: How Much Weight Each Tire Can Carry
Right after the size code you will see a two or three-digit number. This is the load index, a shorthand for the maximum weight each tire can safely carry when properly inflated. Cars typically use load indexes in the range of 75 to 100.
As an illustrative example: a load index of 94 equals 1,477 pounds per tire, which is typical for a midsized car. Four tires at that rating support a combined maximum of 5,908 pounds (4 × 1,477). Your actual vehicle weight must stay below that combined figure.
Light-truck tires also carry a load range letter (B, C, D, E, and so on) that indicates ply rating and maximum load capacity. Load range E, for instance, corresponds to a 10-ply rating.
Speed Rating: The Maximum Safe Speed
The letter immediately after the load index is the speed rating. It represents the maximum speed the tire can sustain while carrying the load defined by the load index. Common ratings you will see on US passenger tires:
| Letter | Max Speed | Typical Use |
|---|---|---|
| Q | 99 mph | Some winter/snow tires |
| R | 106 mph | Winter/snow tires |
| S | 112 mph | Truck all-season |
| T | 118 mph | Standard all-season |
| H | 130 mph | All-season, SUV |
| V | 149 mph | All-season, performance |
| W | 168 mph | Ultra-high-performance |
| Y | 186 mph | Ultra-high-performance |
Never replace a tire with one that has a lower speed rating than the original equipment specification. A higher rating is acceptable and will not harm the vehicle.
DOT Date Code: How Old Is Your Tire?
Somewhere on the sidewall you will find a string beginning with DOT. The last four digits of that string are the manufacture date code, and they are the most safety-relevant numbers on the tire.
The first two digits are the week of the year, and the last two are the final two digits of the year. So 0424 means the tire was made in the 4th week of 2024. As an example, a code of 1319 means the 13th week of 2019.
Tires made before 2000 used only three digits, making the decade ambiguous. If you find a three-digit date code, the tire is at least 25 years old and should be replaced immediately regardless of tread depth.
Rubber breaks down over time, even when a tire looks fine. Check the date code on your spare too, because spares age while sitting. For a deeper look at measuring tread depth alongside tire age, both factors matter for replacement decisions.
UTQG Grades: Treadwear, Traction, and Temperature
All passenger car tires sold in the United States since 1979 are required by federal law to carry Uniform Tire Quality Grading (UTQG) ratings. You will see three values molded into the sidewall, reading something like Treadwear 400 Traction A Temperature B.
Treadwear Grade
This is a comparative number, not a mileage promise. A tire graded 200 is expected to last twice as long on the government test course as one graded 100. Higher numbers suggest longer wear life under controlled conditions, but actual wear depends on driving habits, road surfaces, and maintenance. Importantly, the grades are assigned by the tire manufacturers themselves based on their own test results; NHTSA does not conduct the tests, though it can audit the data.
Traction Grade
Traction grades run from highest to lowest: AA, A, B, C. They measure the tire’s ability to stop on wet pavement in a straight line at 40 mph on government test surfaces of asphalt and concrete. This test does not measure cornering, hydroplaning resistance, or dry stopping. A tire rated AA stops shorter on wet roads than one rated A or B.
Temperature Grade
Temperature grades (A, B, C) reflect how well the tire resists heat buildup at speed. Grade A handles speeds above 115 mph. Grade B covers 100 to 115 mph. Grade C covers 85 to 100 mph. Any tire that cannot reach grade C cannot legally be sold in the United States.
Other Markings Worth Knowing
Several extra symbols appear on sidewalls. Each one carries real meaning for safety and fit:
- M+S or M&S: Mud and Snow. This marking means the tire meets the all-season definition set by the Rubber Manufacturers Association, a trade group for tire makers. It is common on all-season tires but does not promise strong performance in heavy snow.
- 3PMSF (Three Peak Mountain Snowflake): The tire has passed a severe-snow traction test. This is a stronger winter-capability claim than M+S alone.
- Directional arrow: Some tread patterns are built to spin in one direction only. The arrow on the sidewall shows which way the tire must turn when the car moves forward. Putting a directional tire on backward hurts wet-road performance.
- XL or Extra Load: The tire is built to handle higher inflation pressures and heavier loads than a standard-load tire of the same size.
- RFT or ZP: Run-flat tire. These tires have reinforced sidewalls. That means you can keep driving for a limited distance after losing air pressure. The maker sets the exact speed and distance limit.
- TWI (Tread Wear Indicator): A triangle or small icon on the sidewall marks the location of raised wear bars inside the tread grooves. When the tread surface is flush with those bars, the tire has reached its wear limit.
The Pressure Number on the Sidewall Is Not Your Target
Consumer Reports says to check the door-jamb placard if you bought a used car. A past owner may have put on tires that do not match the original spec.
Frequently asked questions
What does the 'P' prefix mean, and does it matter if my replacement tire omits it?
P stands for passenger vehicle. It affects how load and speed ratings are figured out. A non-P, or Euro-metric, tire of the same size carries a slightly different load at the same air pressure. If your original tire had a P prefix, swapping it for a non-P tire can change the effective load rating. Check your owner's manual or door-jamb placard before making that swap.
How do I find the DOT date code if I can't see it easily?
The full DOT string, including the four-digit date code at the end, is molded on one side of the tire. If you cannot see it on the outer sidewall, try looking at the other side or use a flashlight. The last four digits show the week and year the tire was made.
Do UTQG treadwear grades let me predict how many miles a tire will last?
Not reliably. The treadwear grade compares wear on a government test course. It is not a mileage promise. Real wear depends on driving style, road conditions, inflation, alignment, and rotation habits. Makers set their own grades. Use the grade for rough comparisons within a brand's lineup, not as a mileage target.
What does the traction grade actually test, and what does it miss?
The UTQG traction test measures straight-line wet stopping at 40 mph on asphalt and concrete with the brakes locked. It does not measure cornering grip, hydroplaning resistance, acceleration traction, or dry-road stopping. A tire rated AA stops shorter on wet pavement in a straight line than one rated A, but the grade says nothing about how the tire handles a wet curve.
My tire has plenty of tread left but the date code shows it is 8 years old. Should I replace it?
Age matters on its own, apart from tread depth. Rubber oxidizes over time, weakening the tire's inner structure even when the surface looks fine. An 8-year-old tire should get a professional check at the very least. Ask a tire specialist whether it is still safe to use, since visible tread alone does not tell the whole story.
Sources
- Tire code - Wikipedia · en.wikipedia.org
- Uniform Tire Quality Grading - Wikipedia · en.wikipedia.org
- Choose the Right Tires for Your Vehicle · Consumer Reports (consumerreports.org)
Prepared from these references and checked against them. References retrieved October 11, 2026.
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