How To Read Tire Numbers And Letters | Decode The Sidewall

Tire sidewall codes show size, load rating, speed symbol, build type, and age, so you can match a tire to your vehicle.

A tire sidewall looks crowded until you know the reading order. Start at the main size line, move left to right, and each block falls into place. After a few tries, you can spot the tire category, width, wheel size, load rating, speed class, and build date in less than a minute.

That matters when you’re replacing one tire, shopping a full set, or checking a used car. A sidewall can tell you whether the tire fits the wheel, whether it can carry the vehicle’s weight, and whether it was built years ago or last season.

Reading Tire Numbers And Letters On A Standard Sidewall

Use a common code like P225/65R17 102H. That single line gives you the core facts.

• P = passenger tire
• 225 = width in millimeters
• 65 = sidewall height as a share of width
• R = radial construction
• 17 = wheel diameter in inches
• 102 = load index
• H = speed symbol

That’s the line to find first. The rest of the sidewall adds detail around it, such as winter marks, treadwear grades, and the DOT date code.

What The Opening Letter Means

P means passenger. LT means light truck. ST is for trailer tires. T often marks a temporary spare. Some tires start with no letter. The size still reads the same way, though the intended use can vary by brand or market.

Match this opening code before anything else. A trailer tire is not a passenger-car tire, even if the rest of the size looks close.

Width, Aspect Ratio, Construction, And Rim Size

The width is the three-digit number in millimeters. The aspect ratio is the next number. A 65-series tire has a sidewall height equal to 65% of its width. Lower ratios mean shorter sidewalls. Higher ratios mean taller sidewalls.

The construction letter is usually R for radial. Then comes wheel diameter. A tire marked 17 fits a 17-inch wheel. That number must match exactly.

Load Index And Speed Symbol

The load index is a coded number tied to carrying capacity. The speed symbol is a letter tied to the tire’s tested top-speed class. When you buy replacements, match or exceed the vehicle maker’s required load and speed ratings unless your placard or manual lists another approved setup.

On some light-truck tires, you may see two load numbers, such as 124/121. That split code points to different load ratings for single and dual applications. Passenger tires usually show one load index.

What The Extra Sidewall Marks Tell You

After the main size line, scan the smaller marks. These often decide whether two tires that look alike on a shopping page are actually the same thing.

UTQG Grades

Many passenger tires sold in the United States also show treadwear, traction, and temperature grades under the Uniform Tire Quality Grading System. Treadwear is a comparison grade, not a mileage promise. Traction grades run from AA down to C for straight-line wet braking. Temperature grades run from A down to C for heat resistance.

Use these grades to compare similar tire types, not totally different ones. A touring all-season tire and a dedicated winter tire are built for different jobs.

DOT Code And Tire Age

The DOT code helps you read age. On one sidewall, you’ll see a longer string ending in four digits. NHTSA’s Tire Buyers’ FAQ says those last four digits show the week and year the tire was made. A code ending in 3424 means the 34th week of 2024.

This is handy when you’re buying a tire that has sat in storage or checking an older spare. Age belongs in the same check as tread depth, cracking, bulges, and uneven wear.

XL, M+S, And The Snowflake Symbol

XL means extra load. M+S means mud and snow. The 3PMSF symbol, the three-peak mountain snowflake, marks a tire that passed a snow-traction test standard. If winter driving matters where you live, that symbol tells you more than M+S alone.

You may also see marks like Tubeless or brand names for run-flat designs. Read those after you’ve confirmed size, load, speed, and age.

Marking	Meaning	Check
P	Passenger tire	Use on cars and many crossovers
LT	Light truck tire	Built for truck-style loads
225	Width in mm	Stay in the approved size range
65	Aspect ratio	Changes sidewall height
R	Radial construction	Standard road-tire format
17	Wheel size in inches	Must match the rim
102	Load index	Do not go below spec
H	Speed symbol	Match the approved class
DOT	ID and compliance code	Last four digits show age

How To Match Tire Numbers To Your Vehicle

The best reference point is not always the tire already on the car. It’s the placard on the driver-side door jamb and the owner’s manual. That placard lists the original size and the cold inflation pressure chosen by the vehicle maker.

Use this order when you check fitment:

1. Read the door-jamb placard.
2. Match wheel diameter exactly.
3. Match or exceed the required load index.
4. Match or exceed the required speed symbol when called for.
5. Set inflation by the placard, not the sidewall maximum.

The sidewall often lists a maximum load and a maximum pressure tied to that load. That is not your daily pressure target for normal driving unless the vehicle maker says so.

Sample Code	Read It As	Meaning
P215/55R17 94V	Passenger, 215 mm, 55-series, 17-inch, 94V	Common car-tire format
LT265/70R18 124/121S	Light truck, 265 mm, 70-series, 18-inch, heavy load rating	Truck tire with higher carrying duty
235/45R18 98Y XL	18-inch radial with extra-load rating	Same size can come in XL form
T125/70D17 98M	Temporary spare with narrow tread	Spare-use tire
225/65R17 102H M+S	Passenger-size radial with mud-and-snow mark	Common all-season code
245/40R19 98V 3PMSF	Performance size with snowflake symbol	Winter-test mark adds context

When A Different Size Can Work

People change tire size for wheel swaps, winter setups, or ride comfort. That can work if the overall diameter stays close, the tire clears the body and suspension, and the wheel width suits the tire. Load rating and speed symbol still need to stay in range.

A small width change does not tell the whole story. Two tires can share a width and still differ in height, weight rating, or rim fit. Read the full code every time.

Mistakes That Trip People Up

A few sidewall mix-ups keep showing up:

• Using max PSI as the everyday setting. Use the door-jamb placard unless you have a special load case and a matching spec.
• Reading load index as pounds. It is a code, not a direct weight label.
• Treating M+S as a full winter stamp. The snowflake symbol says more.
• Skipping the date code. A tire with good tread can still be old.
• Matching width but missing diameter. The wheel-size number must line up.
• Assuming the current tire is right. Used cars often arrive with mixed sizes or ratings.

If you read the line in order, most of these mistakes disappear. Start at the first letter, move through width and aspect ratio, then finish with construction, rim size, load index, and speed symbol.

A 30-Second Way To Read Any Tire

When you’re in a shop or scrolling a listing, use this short routine:

1. Find the main size line.
2. Read the tire category.
3. Read width, aspect ratio, and construction.
4. Confirm wheel diameter.
5. Check load index and speed symbol.
6. Scan for XL, M+S, or 3PMSF if those matter to you.
7. Find the DOT code and read the last four digits for age.

Once you know the pattern, the sidewall stops looking like alphabet soup. You can spot a wrong listing in seconds, compare similar tires with a clearer eye, and buy the right size with less guesswork.