Tire sidewall numbers show width, profile, construction, wheel size, load index, speed rating, and the week and year it was made.
A tire code looks messy at first glance. Once you know the pattern, it reads like a label. That matters when you’re buying replacements, checking tire age, or matching what your car came with from the factory.
Most drivers spot the size and skip the rest. Then a shop asks about load index, speed rating, or the DOT date stamp, and the sidewall suddenly feels harder than it is. Read it once, and you’ll stop guessing.
Why The Sidewall Tells You More Than Size Alone
Your tire sidewall is a compact spec sheet. It tells you width, sidewall profile, build type, and wheel diameter. It can also show passenger or light-truck class, load index, speed rating, seasonal marks, original-equipment marks, and the DOT code with the week and year the tire was built.
That extra detail matters. A tire can match your wheel diameter and still be the wrong choice if its load or speed rating falls short. Reading the full sidewall helps you catch that before you buy.
How To Read Tire Code On Any Passenger Car Tire
Take a common string like P225/45R17 94W. Read it from left to right. Each chunk adds one piece of the tire’s spec.
Start With The Service Type
The first letter can show the tire’s class. P means passenger tire. LT means light truck. ST is used on special trailer tires. Some tires skip the opening letter and start with the width.
Read The Width And Aspect Ratio
In 225/45R17, the 225 is the section width in millimeters. The 45 is the aspect ratio, which means the sidewall height is 45 percent of the width.
Lower aspect-ratio tires usually have shorter sidewalls and a firmer feel. Higher ratios usually bring more sidewall height and a softer ride.
Find The Construction And Wheel Diameter
The R means radial construction. That’s the standard on modern passenger vehicles. The 17 means the tire fits a 17-inch wheel.
This is a common mix-up: width and wheel diameter do not make a full tire size by themselves. The aspect ratio has to match too.
Finish With Load Index And Speed Rating
The 94W part is the service description. 94 is the load index, a coded number tied to how much weight one tire can carry when inflated properly. W is the speed rating, a coded letter for the tire’s tested speed class.
Michelin’s sidewall markings page uses the same left-to-right format and is a handy cross-check when you’re staring at your own tire in the driveway.
When you replace tires, match the vehicle placard and owner’s manual first. Then compare what’s on the sidewall.
| Marking | What It Means | Why You Should Care |
|---|---|---|
| P | Passenger tire class | Separates passenger fitments from light-truck or trailer tires |
| 225 | Section width in millimeters | Affects fit, clearance, and the contact patch shape |
| 45 | Aspect ratio | Changes sidewall height, ride feel, and wheel protection |
| R | Radial construction | Shows the tire’s internal build type |
| 17 | Wheel diameter in inches | Must match the wheel exactly |
| 94 | Load index | Shows how much weight one tire can carry at the right pressure |
| W | Speed rating | Shows the tire’s tested speed class |
| XL | Extra Load | Shows higher load capacity than standard load in the same size |
| M+S or 3PMSF | Seasonal traction marks | Helps you spot basic mud-and-snow branding or severe-snow certification |
Marks That People Misread All The Time
Once the size code clicks, the rest of the sidewall gets easier. These markings often sit in different spots, so you may need to scan around the tire.
DOT Date Code
The DOT Tire Identification Number ends with four digits that show when the tire was built. The first two digits are the week. The last two are the year. So 2324 means the 23rd week of 2024.
That matters when you’re buying shelf stock or checking an older spare. NHTSA’s tire safety ratings page says the last four digits of the TIN show the week and year of manufacture, and it notes that the full code may not appear on both sidewalls.
Max Pressure Is Not Your Daily Pressure
The sidewall may list a maximum load and maximum inflation pressure. That is not your normal cold tire pressure. Your regular target comes from the vehicle placard, usually on the driver’s door jamb.
If the placard says 35 psi, filling to the sidewall max just because it’s printed on the tire is the wrong move for everyday driving.
UTQG Grades
Passenger tires sold in the U.S. often carry Uniform Tire Quality Grading marks for treadwear, traction, and temperature. A higher treadwear number points to a longer relative wear rate in that test system. Traction grades run from AA down to C. Temperature grades run from A down to C.
These grades help when you’re comparing passenger tires in the same class. They do not tell the whole story on ride, noise, steering feel, or wet grip outside the test method.
M+S And 3PMSF Are Not The Same Mark
M+S stands for mud and snow. 3PMSF, the three-peak mountain snowflake symbol, means the tire passed a winter traction test. If snow is part of your winter, that difference matters.
| Sidewall Mark | Plain-English Meaning | What To Do With It |
|---|---|---|
| 2324 | Built in week 23 of 2024 | Use it to check tire age when buying or inspecting |
| MAX LOAD / MAX PRESS | Upper limit for that tire | Do not treat it as your normal cold pressure target |
| UTQG 500 A A | Treadwear, traction, temperature grades | Use it to compare passenger tires in the same category |
| 3PMSF | Severe-snow winter traction mark | Look for it if you drive in true winter conditions |
| OE Marking | Factory-approved spec for a certain model | Match it if your car depends on a brand-specific tire tune |
What To Match Before You Order New Tires
If you’re replacing tires, don’t stop at the first big number you see. Match the full size, then compare the service description and any marks your car may depend on.
Check the car before you check the catalog. The placard on the driver-side door jamb is the fastest way to confirm the factory size and pressure target. The owner’s manual backs that up and may list alternate fitments for trims, wheel packages, or winter setups.
Some vehicles use the same size at all four corners. Others do not. A staggered setup may use one size in front and another in back. Temporary spares are their own thing too, so don’t use the compact spare as your shopping reference for a full set.
- Check the placard first. The driver-door sticker gives the factory tire size and pressure target.
- Match wheel diameter exactly. A 17-inch tire does not fit an 18-inch wheel.
- Meet or exceed the load index. Dropping lower can put the tire outside the car’s needs.
- Meet or exceed the speed rating. This matters on performance trims.
- Check the build date on older stock. The date should never be a mystery.
- Look for winter marks if your weather demands them. M+S and 3PMSF are not interchangeable.
Tire size changes are not just a styling move. A different size can change gearing feel, speedometer accuracy, ride quality, and clearance inside the wheel well. If you’re changing size on purpose, run the numbers before you buy.
Reading Tire Code Gets Easy After The First One
Most tire codes follow the same rhythm: type, width, profile, construction, wheel size, then service description. After that, scan the rest of the sidewall for the DOT date, seasonal marks, UTQG grades, and any load or OE notes.
Read your own tire once today. After that, the sidewall stops looking random. You’ll know what fits, what the tire can carry, how old it is, and which marks deserve a closer look.
References & Sources
- Michelin.“How to Read Tire Markings and Sidewall Codes.”Explains how tire width, aspect ratio, construction, wheel diameter, load rating, speed rating, and date code appear on the sidewall.
- National Highway Traffic Safety Administration.“Tire Safety Ratings and Awareness.”Shows how NHTSA describes UTQG grades, replacement guidance, tread limits, and the DOT Tire Identification Number date code.