Read the Numbers on Your Tire, From Size to Birth Date
A wall of numbers on the side of your tire. Six reads tell you what it is, how old it is and if it belongs on your car.
Story in Brief
- In 225/65R17 102H, 225 is width in millimeters, 65 is sidewall height as a percent of width, and 17 is rim size in inches.
- 102 means 1,874 pounds per tire on Michelin's chart. H means 130 mph.
- The last four digits of the DOT code are the build week and year. 2524 is week 25 of 2024.
- Federal rules only make the full code show up on one side, so check the inner face too.
- MAX PRESS on the tire is a limit, not your target. Your door label gives the right number.
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Tools and Parts for This Job
- Flashlight
- Phone camera, to shoot the inner side of the tire
- Paper or a note app
- Tread depth gauge or a penny
- Your door label or owner manual
Specs for This Job
| Item | Spec |
|---|---|
| Date code | 4 digits, week then year. 49 CFR 574.5 |
| Sidewalls that must show the code | At least one. 49 CFR 574.5 |
| Door label location | Driver side B pillar. 49 CFR 571.110 |
| Tread wear bars show at | 2/32 inch, 1.6 mm. Michelin |
| Age limit advice | Some makers say 6 to 10 years. NHTSA. Close look at 5, replace by 10. Michelin |
| Load index example | 91 is 1,356 lb. 102 is 1,874 lb. Michelin chart |
| Speed rating example | H is 130 mph. V is 149 mph. Michelin chart |
Look at the side of your tire. You will see a long string like 225/65R17 102H, plus a DOT code and words like MAX PRESS. Michelin reads that first string as six separate facts. Most of the rest tell you how old the tire is, how much it can carry and how fast it can safely go.
You need these numbers for three things. They help you buy the right replacement. They tell you if a used tire is too old. They also catch a past owner who put the wrong tire on the car. NHTSA counted 511 deaths in tire related crashes in 2024, so it is worth a few minutes.
The Size String, One Piece at a Time
This table uses the Michelin example. The pounds and mph come from the Michelin load and speed charts.
| Mark | What It Means |
|---|---|
| P or LT in front | P is a passenger tire. LT is a light truck tire with a stiffer build and more load capacity. |
| 225 | Width at the widest point, in millimeters. |
| 65 | Sidewall height, as a percent of width. |
| R | Radial build. |
| 17 | Rim diameter, in inches. |
| 102 | Load index. 1,874 pounds per tire. |
| H | Speed rating. 130 mph. |
Note the mix of units. Width is metric and rim size is in inches. That trips people up when they compare two sizes. As a worked example, using our own math on this size, the sidewall is 225 times 0.65, or about 146 millimeters. That is about 5.8 inches. Add one on top and one on the bottom to the 17 inch rim, and the tire stands about 28.5 inches tall.
The 65 is the piece people misread. It is a percent, not a height. A 225/65 and a 245/65 have different sidewall heights, even with the same number. NHTSA says a number of 50 or lower means a short sidewall, for better steering response and handling.
Read the Tire in This Order
- Start at the door, not the tire. 49 CFR 571.110 puts the label on the driver side B pillar, with the original size and cold pressure. A used car may have the wrong tires on it, so the tire cannot be its own proof. The trap. Some owners read the tire and buy the same wrong size again.
- Read the size string. Compare each piece to the door label. The trap. A flipped digit like 265 for 225 is easy to miss in bad light. Take a photo and zoom in.
- Read the load and speed. Michelin says to match the original load rating and to meet or beat the speed rating. The trap. A higher load index does not raise what your car can carry. Your axle ratings still set that limit.
- Find the date. Look for DOT and read the last four digits. The trap. 49 CFR 574.5 only requires the code on one sidewall, so it may face the inside of the car. Reach around with your phone camera or turn the wheel.
- Find MAX PRESS and ignore it as a target. Michelin says it is the most the tire is built to hold. NHTSA says your target is what the vehicle maker lists. The trap. Filling to the sidewall number can leave the tire well over the right pressure.
- Check the tread. Michelin says wear bars in the grooves mark 2/32 inch. NHTSA gives a penny test, with Lincoln's head upside down. If you can see the top of his head, replace the tire. The trap. Check inner and outer grooves, since wear may be uneven.
The Date Code Is the One Most People Skip
The code is four digits at the end of the DOT string. Federal rules set the first two as the week and the last two as the year. So 0109 is the first full week of 2009. Michelin gives 2524 as week 25 of 2024.
The code tells you when a tire was built, not when it expires. NHTSA says some vehicle and tire makers recommend replacing tires that are 6 to 10 years old, regardless of tread. Michelin says to look closely after 5 years and replace by 10.
That matters most for low mile cars. NHTSA says most drivers wear out the tread before age becomes an issue. The ones at risk own RVs, collector cars, or cars with low yearly miles. A used car with deep tread can still have old rubber, so read the date before you buy. Do the same with a spare. NHTSA warns spares age too, and that a spare is not a replacement for a worn tire.
Load and Speed, in Real Numbers
Letters and index numbers mean little until you see what they stand for. These come from the Michelin charts.
| Load Index | Pounds per Tire |
|---|---|
| 87 | 1,201 |
| 91 | 1,356 |
| 94 | 1,477 |
| 100 | 1,764 |
| 102 | 1,874 |
| 110 | 2,337 |
| Speed Rating | Top Speed |
|---|---|
| S | 112 mph |
| T | 118 mph |
| H | 130 mph |
| V | 149 mph |
| W | 168 mph |
| Y | 186 mph |
Note the order of the speed letters. H sits below V, so the alphabet does not help here. An XL mark means the tire is built to carry more than a standard tire of the same size, per Michelin, and it should be replaced with an equal spec.
The Other Marks Worth Knowing
Most passenger tires also carry three government grades. 49 CFR 575.104 explains them. Treadwear is a comparison on a test course, so a 150 wore one and a half times as well as a 100 there. It is not a mileage promise. Real wear depends on your driving, roads and climate.
Traction runs AA, A, B and C, from best to worst, for straight line stopping on wet pavement. It does not cover cornering or hydroplaning. Temperature runs A, B and C, and C is the level all passenger tires must meet.
Snow marks differ too. Michelin says M+S is the maker's own call and needs no standard test. The Three Peak Mountain Snowflake needs a passed traction test on snow. That matters if your state or a mountain road has winter rules.
Once you know your numbers, you can spot a bad deal or a wrong fit. See more home checks in our DIY guides, and look up campaigns by make in the recall tracker.
When to Stop and Call a Mechanic
- You see a bulge, cut or crack. NHTSA says to stop using a tire with signs of physical damage.
- The size or load rating on the tire does not match your door label. Have a tire shop look before you drive far.
- The tread is at the wear bars, or you can see the top of Lincoln's head in the penny test.
- The DOT date is over 10 years old on a tire you plan to keep using.
- The tire keeps losing air, or it makes a noise or vibration. NHTSA says to see a tire professional.
Reader Mail
- What do the numbers on a tire mean?
- Take 225/65R17 102H. Michelin reads it as 225 millimeters wide, a 65 percent sidewall, radial, a 17 inch rim, load index 102 and speed rating H.
- How do I tell how old my tire is?
- Find the DOT code and read the last four digits. Federal rules make those the week and then the year, so 0109 is the first full week of 2009. It may be on the inner side only.
- Where do I find the right tire size for my car?
- Look at the label on the driver side door post. 49 CFR 571.110 requires the original tire size on it, along with the cold pressure. Your manual has it too.
- Should I fill my tires to the number on the sidewall?
- No. NHTSA says the correct pressure is what the vehicle maker listed, not what is on the tire. Michelin calls the sidewall number a maximum.
- Can I put a different speed rating on my car?
- Michelin says replacements should meet or exceed the speed rating the maker specified. A lower rating is not advised unless it is a winter tire marked 3PMSF, and then you must stay under its limit.
Record and Data Links
- 49 CFR 574.5, Tire Identification Requirements, National Highway Traffic Safety Administration
- 49 CFR 571.110, Federal Standard No. 110, Tire Selection and Rims, National Highway Traffic Safety Administration
- 49 CFR 575.104, Uniform Tire Quality Grading Standards, National Highway Traffic Safety Administration
- TireWise, Tire Safety Ratings and Awareness, National Highway Traffic Safety Administration
- How to Read Tire Markings and Sidewall Codes, Michelin
- Choose the Right Tire, Load and Speed Charts, Michelin
- Tire Load Rating and Speed Rating Explained, Michelin