How To Read Tire Sidewall Codes | Decode Every Mark

Tire sidewall markings show size, load index, speed rating, age, and construction, so you can match a tire to your vehicle.

A tire’s sidewall is a compact label wrapped around rubber. It tells you whether a tire fits your wheel, how much weight it can carry, how fast it is rated to run, when it was made, and what kind of weather it is built for. Once you know the pattern, the string of letters and numbers stops looking cryptic.

That matters when you buy replacements, compare two tire quotes, or check the spare in your trunk. A tire can share the same width and rim diameter as another tire and still be a poor match because the load index, speed rating, or winter marking is off.

How To Read Tire Sidewall Codes On Any Passenger Tire

Start with a common size line such as 225/45R17 94W XL. Read it left to right. Each chunk tells you one part of the tire’s job.

• 225 = section width in millimeters
• 45 = aspect ratio, or sidewall height as a share of width
• R = radial construction
• 17 = wheel diameter in inches
• 94 = load index
• W = speed rating
• XL = extra-load casing built to carry more weight at the proper pressure

Some tires add a prefix before the size. P means passenger. LT means light truck. T marks a temporary spare. If your door placard calls for an LT tire, replacing it with a passenger tire that merely “fits” is not a like-for-like swap.

What The Size Block Tells You

The first four pieces decide physical fit. Width and aspect ratio set the tire’s shape. The construction letter tells you how the internal cords are laid out. The wheel diameter must match the rim exactly. A 17-inch tire does not stretch onto an 18-inch wheel, no matter how close the rest of the code looks.

Aspect ratio trips people up more than any other number. A 225/45R17 and a 225/55R17 share the same width and rim diameter, yet the second tire has a taller sidewall. That changes overall diameter, ride feel, speedometer accuracy, and wheel-well clearance.

What The Service Description Tells You

The load index and speed rating sit near the end of the size line. Michelin says this pair is the tire’s service description, and it must meet or exceed the vehicle maker’s spec when you replace a tire. If your placard calls for 94W, dropping to 91V just because the tire is cheaper is a bad trade.

Load index is not a weight in pounds printed in plain text. It is a code tied to a load table. Speed rating is a letter code tied to a test standard. You do not need to memorize the whole chart. You do need to match the rating on the placard, owner’s manual, or the original tire.

Markings Many Drivers Miss The First Time

Sidewalls carry more than the size line. You may also see MAX LOAD, MAX PRESS, M+S, the mountain-snowflake symbol, TUBELESS, ROTATION, or OUTSIDE and INSIDE. Each one adds context.

MAX LOAD and MAX PRESS are often read the wrong way. They show the tire’s upper load and pressure limits, not the pressure you should use day to day. For normal inflation, use the vehicle placard on the driver’s door jamb or the owner’s manual. Michelin’s page on tire sidewall markings says the same thing.

M+S means the tread design is meant for mud and snow use under the maker’s own criteria. The 3PMSF symbol, shown as a mountain with a snowflake, is a tougher winter mark tied to a snow-traction test. If you drive in steady cold and snow, that difference is worth checking before you buy.

Marking	What It Means	Why It Matters
P	Passenger tire	Matches passenger-car fitment and load class
LT	Light-truck tire	Built for truck and van loads, often with a stronger casing
T	Temporary spare	Use only as a short-term spare, not a full-time replacement
XL or Reinforced	Extra-load construction	Carries more load than a standard-load tire of the same size
M+S	Mud and snow marking	Signals all-season style tread, though not a passed snow test
3PMSF	Three-Peak Mountain Snowflake	Shows the tire passed a standardized winter-traction test
ROTATION	Directional tread	Tire must roll in the marked direction for proper water evacuation
OUTSIDE / INSIDE	Asymmetric tread mounting marks	Tells the installer which side faces outward
MAX LOAD	Upper load limit	Not the same thing as your car’s normal operating load
MAX PRESS	Upper inflation limit	Not the same thing as the door-placard pressure

Reading The DOT Code And Tire Age

Near the bead, you will find a DOT code. The last four digits show the week and year the tire was made. A tire ending in 0924 came from the ninth week of 2024.

This date helps when you compare stock at a shop, inspect an old spare, or check all four tires on a used car. Age alone does not tell the whole story. Storage, heat, inflation, and wear still matter. Still, the DOT date gives you a clean starting point that any buyer can read in seconds.

The full DOT string is longer than the date code. It also includes plant and tire-identification data used in recalls and traceability. You do not need to decode each character for routine shopping, though it is smart to make sure the DOT marking is present and legible on the sidewall.

UTQG Grades: Treadwear, Traction, Temperature

Many passenger tires sold in the United States also show UTQG grades. NHTSA says the Uniform Tire Quality Grading System covers treadwear, traction, and temperature resistance on passenger tires. Those grades give you another way to compare two tires that share the same size.

A higher treadwear number points to longer relative wear in the UTQG test. Traction grades run from AA down to C. Temperature grades run from A down to C. These marks work well for side-by-side shopping, though they are not a full picture of ride comfort, noise, wet braking feel, or winter grip.

Sidewall Piece	Read It Like This	Check Before You Buy
225/45R17	Width, aspect ratio, radial, 17-inch rim	Must match the wheel and clear the car properly
94W	Load index and speed rating	Must meet or exceed the placard spec
XL	Extra-load casing	Match it if the original tire uses it
DOT 0924	Made in week 9 of 2024	Useful when checking stock age or an old spare
UTQG 500 AA A	Treadwear 500, traction AA, temperature A	Good for comparing passenger tires in the same size

What Must Match On Replacement Tires

If you want a safe replacement, match the size first, then check the service description, then confirm any special marks. This short list keeps you out of most trouble:

• Match the wheel diameter exactly.
• Stay with the placard size unless you are making a planned wheel-and-tire change.
• Meet or beat the original load index and speed rating.
• Match XL, Reinforced, Run Flat, or OE marks when your vehicle was built around them.
• Use the right seasonal symbol for your weather and driving pattern.

Do not set pressure from the number molded next to MAX PRESS. Use the vehicle placard. Do not assume two tires with the same width and rim diameter are interchangeable. And do not ignore inside-outside or rotation arrows during installation.

Common Sidewall Reading Mistakes

Most mix-ups come from rushing. A few show up so often that they are worth naming plainly.

1. Mixing up rim diameter and overall tire height. The last number in the size line is the wheel diameter, not the tire’s outer height.
2. Treating max pressure as the daily setting. The placard pressure is the one to use for normal driving.
3. Ignoring load index. Same-size tires can carry different loads.
4. Reading M+S as a full winter rating. Check for the 3PMSF mark if winter grip is part of the plan.
5. Forgetting the DOT date on the spare. A spare can look new and still be old.

Using Tire Sidewall Markings With Confidence

When you read the sidewall in order—size, service description, special marks, then DOT date—the code starts to feel plain. You are not trying to become a tire engineer. You are checking fit, load, speed, weather use, and age with enough clarity to buy the right tire and ask sharper questions at the shop.

The next time you stand next to your car, read one tire from left to right and compare it with the placard on the driver’s door. In two minutes, the sidewall stops being a wall of characters and turns into a clean buying checklist.