Tire sidewall codes show width, sidewall profile, construction, wheel size, load index, speed rating, and the week and year the tire was made.
If the string on your tire looks like a secret code, you’re not alone. A sidewall packed with letters and numbers can feel messy at first, yet the pattern is steady once you know the order.
That matters when you’re shopping for replacements, checking fitment, or trying to avoid paying for the wrong set. One line on the sidewall tells you how wide the tire is, how tall the sidewall stands, what wheel it fits, how much weight it can carry, and the speed class it was built for.
Most passenger tires follow the same layout. Read it left to right, and each chunk falls into place.
How To Read Tire Numbers On A Sidewall
Take a sample code like P225/45R17 94V. That single line gives you the tire type, width, aspect ratio, construction, wheel diameter, load index, and speed rating.
Here’s the order most drivers will see on a passenger tire:
- P = passenger tire
- 225 = tire width in millimeters
- 45 = sidewall height as a percentage of width
- R = radial construction
- 17 = wheel diameter in inches
- 94 = load index
- V = speed rating
Once you know that pattern, most tire codes stop looking intimidating. The trick is not reading the line as one long number. Read it in blocks.
Start With The Prefix
The first letter tells you what kind of tire you’re dealing with. On many cars, you’ll see P for passenger. Light trucks often use LT. Temporary spares often start with T.
No prefix at all can still be normal. Many tires sold outside North America skip the first letter and start right away with the width.
Read The Three Main Size Pieces
The first three-digit number is the tire width in millimeters. In the sample code, 225 means the tire is about 225 mm wide at its widest point.
The next number is the aspect ratio. That tells you the sidewall height as a percentage of the width. So a 45-series tire has a sidewall height equal to 45% of 225 mm. Lower numbers usually mean a shorter sidewall and a firmer feel on the road.
Then comes the construction letter and wheel size. R means radial, which is what nearly all modern passenger tires use. The 17 means the tire fits a 17-inch wheel.
If one part is off, the whole fit can be wrong. A tire can have the right wheel diameter and still be the wrong width, profile, or load class for your vehicle.
| Marking | What It Means | What To Check |
|---|---|---|
| P | Passenger tire type | Match the tire type your vehicle uses |
| LT | Light-truck tire type | Common on pickups, vans, and heavy-duty use |
| 225 | Section width in millimeters | Wider is not always better for fit |
| 45 | Aspect ratio | Lower number means a shorter sidewall |
| R | Radial construction | Standard on modern passenger tires |
| 17 | Wheel diameter in inches | Must match the wheel exactly |
| 94 | Load index | Do not go below the vehicle requirement |
| V | Speed rating | Meet or exceed the vehicle requirement |
Use The Door Placard Before You Buy Anything
The smartest place to verify tire size isn’t the tire already on the car. It’s the placard on the driver’s door jamb, plus the owner’s manual. Tires get swapped all the time, and the set on your car today may not be the size the car was built around.
NHTSA’s tire buyer page points drivers to the door label and owner’s manual for the correct size. That label also gives the cold tire pressure for the front and rear.
If the sidewall code on your current tire doesn’t match the placard, slow down before ordering replacements. The current set may still fit, yet fit alone doesn’t tell you if the size is right for load, gearing, clearance, or ride height.
Load Index And Speed Rating Matter More Than People Think
The load index and speed rating sit after the size code, and they’re easy to gloss over. Don’t. Two tires can share the same size and still differ in how much weight they can carry or the speed class they’re built for.
A tire marked 94V and one marked 94H are not the same tire in service terms. Same goes for 91V and 94V. The size may match, yet the service description does not.
Michelin’s tire markings page lays out this sequence clearly and notes that replacement tires should meet the vehicle maker’s spec. That’s the safe play when you want your car to behave the way it should.
Read The DOT Date Code Too
Near the bead area, you’ll find a DOT code. The last four digits tell you when the tire was made. A code ending in 3524 means the tire came from the 35th week of 2024.
That date is handy when you’re buying tires that have been sitting in storage or checking an old spare. On many tires, the full date code appears on only one sidewall, so you may need to look at both sides.
| Extra Marking | Meaning | Why You Might Care |
|---|---|---|
| DOT 3524 | Made in week 35 of 2024 | Lets you check tire age |
| M+S | Mud and snow marking | Common on all-season tires |
| 3PMSF | Three-Peak Mountain Snowflake | Shows a winter-performance test mark |
| XL | Extra load tire | Carries more load than a standard-load tire of that size |
| Max Load | Top load rating for the tire | Not the same as your normal vehicle load |
| Max Press | Top inflation figure on the tire | Not your everyday pressure target |
| UTQG | Treadwear, traction, and temperature grades | Common on passenger tires sold in the U.S. |
Common Mistakes When Reading Tire Sidewalls
A few mix-ups show up again and again, and they can lead to a bad purchase.
- Mixing up width and wheel size. A 225 tire is not a 22.5-inch wheel tire. Width is in millimeters. Wheel size is in inches.
- Treating max pressure as the target pressure. The sidewall’s max pressure is not the everyday setting for your car. Use the door placard.
- Ignoring load index. Same size does not always mean same carrying ability.
- Missing the spare-tire prefix. A temporary spare marked with T is not meant for normal full-time driving.
- Reading only one side of the tire. The full DOT date code may be on the inward-facing sidewall.
One more trap: assuming a lower-profile tire is a simple style swap. A shorter sidewall changes the tire’s overall diameter unless the width and wheel size shift in the right way. That can affect clearance and speedometer behavior.
A Simple Way To Decode Any Tire In Under A Minute
When you’re standing in a garage, parking lot, or tire shop, use this order:
- Find the full size code on the sidewall.
- Read the prefix, if there is one: P, LT, T, or none.
- Read the width, then the aspect ratio.
- Find the construction letter and wheel diameter.
- Read the load index and speed rating after the size.
- Check the DOT date code near the bead area.
- Compare all of it with the driver-door placard and manual.
That order works because it keeps the numbers in their own lanes. Width, profile, construction, wheel size, service description, and date code each answer a different question.
Once you’ve done it a couple of times, the line stops looking cryptic. You’ll know whether a tire fits your wheel, whether it matches the car’s spec, and whether the tire is older than you expected before any money changes hands.
References & Sources
- National Highway Traffic Safety Administration (NHTSA).“Tire Buyers’ FAQ—What You Should Know and Ask.”Explains where to find the correct tire size for a vehicle and states that the last four digits of the DOT code show the week and year of manufacture.
- Michelin USA.“Tire Markings Explained: How to Read a Tire.”Breaks down tire type, width, aspect ratio, construction, wheel diameter, load rating, speed rating, pressure markings, and date code.