How To Read Tire Information | Decode The Sidewall

A tire sidewall shows size, load limit, speed rating, and build date so you can match the right tire to your vehicle.

The code stamped on a tire can look dense at first glance, yet it follows a pattern. Once you know the order, you can spot the tire’s width, sidewall height, construction, wheel diameter, load index, speed symbol, and build date in under a minute.

That matters when you’re shopping, checking a used car, or standing in a shop with four near-identical options in front of you. A sidewall can tell you whether a tire matches your door placard, whether it carries enough weight, and whether it’s older than you expected.

How To Read Tire Information On Any Sidewall

Start with the full size string. A common one looks like P225/65R17 102H. Read it left to right, then scan the rest of the sidewall for UTQG grades, load and pressure wording, and the DOT date code.

• P is the tire type.
• 225 is the width in millimeters.
• 65 is the aspect ratio, or sidewall height as a share of width.
• R17 tells you it is a radial tire for a 17-inch wheel.
• 102H is the service description: load index plus speed symbol.

That order stays familiar across most passenger tires, light-truck tires, and many SUV tires. Some marks change by tire type, yet the reading flow stays much the same.

Start With The Size String

The size string is the fastest way to tell whether a tire is even in the right ballpark for your vehicle. If the size on the sidewall does not match the size on the driver’s door placard or the approved alternate size in your owner’s manual, stop there and double-check before you buy.

What The Prefix Means

The first letter tells you the tire’s class. P means passenger. LT means light truck. ST is for trailers, and T marks a temporary spare. No prefix can still appear on some metric tires. That does not mean the rest of the code loses meaning; it only means the type is shown a bit differently.

What The Numbers Mean

Take 225/65R17. The 225 is the section width in millimeters. The 65 is the aspect ratio, so the sidewall height equals 65 percent of the width. The R means radial construction, which is what you will see on nearly all modern road tires. The 17 is the wheel diameter in inches.

One common slip is mixing up wheel diameter with total tire diameter. A 17-inch marking does not tell you the tire stands 17 inches tall. It only tells you the wheel size the tire fits.

Read The Service Description Next

The service description sits after the size. In 102H, the 102 is the load index and the H is the speed symbol. Load index is not a weight number by itself; it points to a chart. The speed symbol tells you the top speed category the tire is built for under set test conditions.

This part deserves a slow read. Two tires can share the same size and still differ in load index or speed symbol. If you swap in a lower spec than your vehicle calls for, you may end up with a tire that is not suited to the job.

Sidewall Mark	What It Means	What To Check
P / LT / ST / T	Tire type: passenger, light truck, trailer, or temporary spare	Match the tire to the vehicle’s use
225	Section width in millimeters	Stay with the approved width range
65	Aspect ratio, or sidewall height as a share of width	Lower numbers change ride and clearance
R	Radial construction	Common on modern road tires
17	Wheel diameter in inches	Must match the wheel exactly
102	Load index	Do not drop below the placard spec
H	Speed symbol	Match or exceed the vehicle’s required rating
Max Load / Max Pressure	Upper limits printed on the tire	Do not use this in place of door placard pressure
UTQG	Treadwear, traction, and temperature grades on many passenger tires	Use for same-category comparisons
DOT + 4 digits	Plant code and build date	Read the last four digits for week and year

What UTQG Grades Tell You Before You Buy

Many passenger tires sold in the United States carry UTQG grades on the sidewall. The three pieces are treadwear, traction, and temperature. NHTSA’s tire safety ratings page lays out how these grades work and where they fit in tire shopping.

Treadwear is a comparative grade, not a mileage promise. A 600 grade is expected to last longer than a 300 grade in the UTQG test program, yet that does not mean it will last twice as long on every car, road, or climate. Traction grades run from AA to C. Temperature grades run from A to C. Higher grades are better within that system.

Use UTQG as one filter, not the whole answer. Ride feel, road noise, wet braking, snow grip, and steering response do not boil down to one stamped group of letters and numbers.

Find The DOT Code And Build Date

The DOT string tells you where the tire was made and when it was built. On most tires, the last four digits are the part you want first. They show the week and year of manufacture. A code ending in 2425 means the tire was made in the 24th week of 2025. NHTSA’s Tire Buyers’ FAQ states that the last four digits of the Tire Identification Number show the week and year the tire was made.

You may need to check both sides of the tire to find the full date code. On some tires, the full DOT marking appears on one sidewall, while the other side only shows part of it.

Check the build date on new stock, used tires, and spare tires. Rubber ages even when tread looks fresh. The sidewall date does not tell you when a tire should be replaced by itself, since service life advice can differ by vehicle maker and tire maker, but it does tell you the tire’s starting point.

Sample Code	Read It As	Plain-English Meaning
P225/65R17 102H	Passenger, 225 mm, 65 series, radial, 17-inch wheel, load 102, speed H	A common crossover or sedan tire format
LT275/70R18 125/122S	Light truck, 275 mm, 70 series, radial, 18-inch wheel, dual load indexes, speed S	Built for heavier-duty pickup or van use
ST205/75R15	Special trailer, 205 mm, 75 series, radial, 15-inch wheel	Made for trailers, not tow-vehicle axles
T135/80D16	Temporary spare, 135 mm, 80 series, diagonal construction, 16-inch wheel	Space-saver spare with its own limits
DOT XX XX 2425	DOT serial ending in week 24 of 2025	Shows when the tire was built

Match The Sidewall To Your Vehicle Placard

The tire sidewall tells you what the tire can do. The placard on the driver’s door jamb tells you what your vehicle was built to run. Read them together. If one label says 225/65R17 102H and the other tire shows 225/65R17 98T, the size matches but the service description does not.

• Match the size to the placard or an approved alternate size in the owner’s manual.
• Check load index and speed symbol, not just width and wheel size.
• Use the placard’s cold pressure, even if the tire sidewall shows a higher max pressure.
• Check front and rear values separately if your vehicle uses a staggered setup.

Door Placard Vs Sidewall Pressure

The sidewall’s pressure wording shows the tire’s upper limit at its stated load. That is not the everyday fill number for your car. The placard pressure is set around the vehicle’s weight balance, handling, and ride. Fill to placard pressure when the tires are cold, then recheck them as the seasons change.

Marks That Change By Tire Type

Beyond size and date, you may see a few extra marks that shape how the tire should be used.

• M+S means mud and snow. It is common on all-season tires.
• 3PMSF, the three-peak mountain snowflake symbol, marks a higher winter traction standard than plain M+S.
• XL means extra load. SL means standard load.
• Run Flat or brand-specific wording points to a tire that can travel a limited distance after losing air, under set conditions.
• Rotation with an arrow means the tire must spin in one direction.
• Inside and Outside on an asymmetrical tire show which side faces out when mounted.

Those extra marks are easy to miss when you only read the big size string. That is why a full sidewall scan pays off. One missed word can leave you with the right size and the wrong tire type.

Common Mistakes When Reading A Tire Sidewall

Most shopping errors come from a few repeat slipups.

1. Using the tire’s max pressure as the fill target. The right daily pressure for your vehicle is on the door placard, not the tire’s sidewall max.
2. Matching size but missing load index. Same size does not always mean same carrying ability.
3. Missing the speed symbol. This matters on many cars, crossovers, and performance trims.
4. Buying old stock without checking the DOT date. Tread depth alone does not tell the full story.
5. Putting trailer tires on a tow vehicle. ST tires are built for trailer use.
6. Ignoring directional or inside-outside marks. A tire can be mounted wrong even when the size is right.

If you are comparing online listings, zoom in on the sidewall photo or read the full spec block. If a seller only lists the size and skips the service description, ask for the full sidewall code before you hit buy.

The Sidewall Is Only Half The Match

A tire sidewall gives you a lot, but not the whole fitment story. The final check is your vehicle placard, owner’s manual, and any approved alternate size listed by the vehicle maker. Wheel width, brake clearance, and trim-specific tire specs can all matter.

Once you know how to read the sidewall, tire shopping gets a lot less fuzzy. You can spot the right size, catch load and speed mismatches, and check the build date before money changes hands. That turns a wall of letters and numbers into a plain, useful label.