How To Read Tire Codes | Decode Size, Load, Speed

Tire sidewall markings show size, load index, speed rating, construction type, and the week and year the tire was made.

If you want to know how to read tire codes, start with the long string molded into the sidewall. In one line, you can spot the tire’s width, profile, build, rim diameter, load index, speed rating, and DOT date code.

That matters when you’re replacing one tire, buying a full set, or sizing up a used tire. Read the code well, and you can weed out a tire that’s too old, too weak for the vehicle, or just the wrong size.

How To Read Tire Codes On Passenger And LT Tires

Take this sample sidewall code: P215/65R17 99H. Read it left to right. The order stays pretty consistent across passenger tires and many light-truck tires.

• P = passenger tire
• 215 = tire width in millimeters
• 65 = aspect ratio, or sidewall height as a share of width
• R = radial construction
• 17 = wheel diameter in inches
• 99 = load index
• H = speed rating

What The First Characters Tell You

The first letter shows the tire type. P means passenger. LT means light truck. ST is used on many trailer tires. Some tires start with no letter at all. Those are often Euro-metric passenger tires, and they still need to match the placard and wheel size.

Why That Prefix Matters

A light-truck tire and a passenger tire can share the same width and rim diameter, yet carry weight in a different way. That’s why a “same size” tire is not always a true swap.

Width, Profile, Construction, And Rim Size

The three-digit number after the prefix is the section width in millimeters. In the sample above, 215 means the tire is 215 mm wide. The next number, 65, is the aspect ratio. It means the sidewall height is 65 percent of the width.

The construction letter is usually R for radial. The next number is the wheel diameter in inches. A tire marked 17 fits a 17-inch wheel.

Load Index And Speed Rating

After the size, you’ll see a number-letter pair such as 99H. The number is the load index. It links to a chart that tells you how much weight one tire can carry when inflated correctly. The letter is the speed rating. It marks the tire’s top tested speed class, not a target for day-to-day driving.

Here’s the plain rule: don’t drop below the vehicle maker’s required load index or speed rating unless the vehicle maker allows it. You can go above.

The Tire Marks Many Drivers Skip

The sidewall has more than the main size line. Some of the most useful clues sit closer to the rim or in a second block of text. These marks help you judge age, weather use, and service class.

One of the biggest is the DOT code. On U.S. road tires, the last four digits of the DOT Tire Identification Number show the week and year the tire was made. A code ending in 0924 means the ninth week of 2024. The date may appear on one sidewall only, so check both sides if you can. NHTSA spells that out in its tire buyers’ FAQ.

You may also spot M+S on an all-season tire or the three-peak mountain snowflake symbol on a tire built for harsher winter grip. Then there are marks such as XL for extra load and load range letters on many LT tires.

Once you can read those extra marks, used-tire ads get easier to sort. You can spot fresh stock, winter-rated rubber, and service class in seconds.

Sidewall Mark	What It Means	What To Check
P / LT / ST	Passenger, light-truck, or trailer service type	Match the vehicle or trailer use listed on the placard or manual
215	Section width in millimeters	Stay with the approved width range for your wheel and vehicle
65	Aspect ratio, or sidewall height as a share of width	Large changes can alter ride height and speedometer reading
R	Radial construction	Match the tire type your vehicle was built to run
17	Wheel diameter in inches	Must match the wheel exactly
99H	Load index and speed rating	Do not drop below the placard or original spec
DOT … 0924	Tire Identification Number with production date	Read the last four digits as week and year
UTQG 600 A A	Treadwear, temperature, and wet-traction grades on many passenger tires	Use it to compare similar replacement tires

Reading A Full Tire Code From Start To Finish

Take a second sample: LT275/70R18 125/122S. Read it in chunks.

1. LT tells you it’s a light-truck tire.
2. 275 is the width in millimeters.
3. 70 is the aspect ratio.
4. R18 means radial construction for an 18-inch wheel.
5. 125/122 is a dual load index setup often seen on LT tires.
6. S is the speed rating.

That double load index trips people up. The first number is often used for single-tire fitment. The second is for dual rear-wheel use.

What UTQG Grades Mean Before You Buy

Many passenger tires sold in the United States also carry UTQG grades. NHTSA says those grades cover treadwear, traction, and temperature on passenger vehicle tires. Treadwear uses a control tire graded at 100. Traction grades run from AA down to C. Temperature grades run from A down to C. You can check the federal rating system on NHTSA’s Tire Safety Ratings page.

Use UTQG to compare tires in the same broad class. It does not tell the whole story on winter grip or ride feel.

Which Tire Codes Should Match Your Vehicle

Your best match point is the tire placard on the driver’s door jamb, fuel door, glove box, or the owner’s manual. That placard gives you the original tire size and cold inflation pressure picked for the vehicle.

When you compare a new tire with the placard, check these items in order:

• Service type: passenger, LT, or trailer
• Wheel diameter
• Load index or load range
• Speed rating
• Overall diameter if you’re changing sizes

If you’re replacing one tire, try to match the brand, model, size, and service description already on the car. Mixing close-but-not-equal codes can leave you with uneven wear and odd behavior in rain or during hard braking.

Sample Code	Read It As	Good Fit When
P205/55R16 91V	Passenger tire, 205 mm wide, 55 profile, 16-inch wheel, 91 load index, V speed rating	Your placard calls for that size and at least that service description
225/45R17 94W XL	Euro-metric passenger tire, 17-inch wheel, extra-load casing, 94 load index, W speed rating	The vehicle spec allows XL or calls for it
LT245/75R17 121/118S	Light-truck tire with higher load class and dual-index marking	You drive a truck, van, or SUV that calls for LT service
ST205/75R14	Trailer tire for a 14-inch wheel	It is mounted on a trailer, not a road vehicle axle
DOT XX XX ABCD 3523	Tire built in the 35th week of 2023	You’re checking age before buying or fitting a used tire

Common Tire Code Mistakes That Cost Money

A lot of bad tire buys start with one of these slipups:

• Reading only the width and rim size. A 225/65R17 and a 225/55R17 both fit a 17-inch wheel, yet their sidewall height and overall diameter differ.
• Ignoring the load index. A cheaper tire can still be the wrong tire if it carries less weight than the vehicle spec.
• Skipping the DOT date. Old stock is not always a bad deal, yet the build date should be part of the price call.
• Mixing passenger and LT tires by guesswork. The letters at the start are there for a reason.
• Using trailer tires on a car or truck. ST tires are built for trailer duty, not drive, steer, or braking duty on a road vehicle.

Read the full line, check the placard, then compare the service description before you pay.

A Simple Way To Check Any Tire In Under A Minute

When you’re standing in a tire shop or scrolling through listings, use this short routine:

1. Find the full sidewall size code.
2. Match the wheel diameter to your wheel.
3. Match the service type to the vehicle.
4. Check the load index and speed rating against the placard.
5. Read the DOT date code.
6. Scan for extra marks such as XL, M+S, or the snowflake symbol.

Once you get the pattern down, tire codes stop looking random. They read like a label with a job description. That makes it easier to buy the right tire the first time and spot a mismatch before it reaches your driveway.