How to Read the Numbers on a Tire

Quick answer: Tire sidewall markings show the tire size (width/aspect ratio), construction type, rim diameter, load index and speed rating; DOT markings record factory and manufacture date. Read the largest numeric group first (the size), then the smaller codes (load index, speed rating), and finish with DOT digits. A worked example and a short checklist below will make this routine simple to follow.

How to read the main tire size group

The largest group of characters on most passenger tires is the size notation. It typically looks like a string such as 205/55R16 or LT245/75R16. Read this group left to right: width, aspect ratio, construction, and rim diameter.

Step-by-step breakdown of the size string

• Width — the first number (for example, 205) is the nominal tread width in millimeters for metric passenger tires.
• Aspect ratio — the number after the slash (for example, 55) is the sidewall height as a percentage of the width. A 55 aspect ratio means the sidewall height is 55% of the tread width.
• Construction — commonly a letter such as R (radial) or B (bias belted). Most modern passenger tires are radial and use R.
• Rim diameter — the final number (for example, 16) is the wheel rim diameter in inches and must match the wheel.

Variations to recognize

Light truck (LT) and metric (P) prefixes change interpretation. An LT at the start (LT245/75R16) means the tire is designed for light trucks and can carry heavier loads at different inflation. A P-prefix (P215/65R15) indicates a passenger tire sized to U.S. P-metric conventions. See the vehicle placard or your owner's manual when matching these types.

Find load index and speed rating

Next to the size you will usually see a two- or three-digit number followed by a letter, for example 91V. The number is the load index; the letter is the speed rating.

Load index

The load index is a coded number that links to a table of maximum load capacity. The number alone is not a weight value; you must consult a chart to translate a load index into pounds or kilograms. For a ready reference, consult a Tire load index chart before selecting replacements.

Speed rating

The alphabetic speed rating (for example H, V, W) denotes the tested maximum sustained speed capability of the tire when properly inflated and loaded. Do not substitute a higher-speed-rated tire without considering handling, ride quality and manufacturer recommendations. For help choosing sizes that match vehicle needs, see Choosing the right tire size.

DOT code and manufacture date

The DOT code begins with the letters DOT and is followed by a string of characters that identify the manufacturer, plant, and production details. The most useful portion for owners is the last four digits on modern tires.

How to read the manufacture date

1. Locate the DOT string on one sidewall; the last four digits in modern tires indicate week and year, written WWYY. For example, 2319 would mean the tire was made in the 23rd week of a year ending in 2019.
2. Older tires (manufactured primarily before 2000) may use a three-digit code; those codes require a different interpretation and often indicate an older tire.
3. If the DOT string is not present or is illegible on an installed tire, remove the tire and inspect both sidewalls; sometimes the DOT is on the inner sidewall.

For decoding help and a lookup utility, use a DOT code lookup tool or consult the tire maker's materials.

Other common sidewall markings and what they mean

• Maximum load and inflation — usually printed as "Max Load" and "Max Pressure"; this is not the recommended operating pressure but the maximum the tire construction can tolerate.
• UTQG numbers — treadwear, traction and temperature grades often appear as a three-part code. These are comparative ratings, not guarantees of life or performance.
• Service type — markings such as M+S (mud and snow) and the 3PMSF (three-peak mountain snowflake) symbol indicate winter capability.
• Run-flat or reinforced — some tires have letters or symbols indicating run-flat technology or reinforced sidewalls.

Step-by-step process: Read a tire sidewall in under two minutes

1. Locate the largest numeric group; read width/aspect/construction/rim diameter (e.g., 205/55R16).
2. Find the short numeric-letter pair following the size to get load index and speed rating (e.g., 91V).
3. Scan for DOT and read the final four digits to find the week and year of manufacture.
4. Note UTQG, M+S or 3PMSF symbols if you need seasonal performance information.
5. Compare the load index and tire type with your vehicle placard or owner's manual before buying or fitting a replacement tire.

Worked example

Suppose a sidewall reads P205/55R16 91V DOT U2LL LMLR 2319.

• P205/55R16 — passenger tire, 205 mm width, 55% aspect ratio, radial construction, 16-inch rim.
• 91V — look up 91 in a load index chart to get the maximum load per tire; V is the speed rating letter.
• DOT ...2319 — the tire was manufactured in the 23rd week of 2019.

Checklist before you buy or fit tires

• Confirm tire size matches your vehicle placard or the sizes approved for your car.
• Verify the load index meets or exceeds the vehicle requirement; consult a Tire load index chart if uncertain.
• Check the speed rating to ensure it is appropriate for your vehicle and driving conditions.
• Check the DOT week/year to avoid buying old-stock tires.
• Note seasonal symbols (3PMSF, M+S) if you need winter capability.

Common mistakes and troubleshooting

• Assuming numbers equal weight — the load index number is a code; do not treat it as kilograms or pounds without using a chart.
• Mixing tire types — installing mismatched construction (radial vs bias) or mixing different load index/speed ratings on the same axle can harm handling.
• Ignoring manufacture date — tires degrade with age even if unused; check the DOT code to avoid old-stock tires.
• Reading only one side — some tires show full DOT only on the inner sidewall; inspect both sides when possible.

Closing: quick decision criteria

When you read the numbers on a tire, prioritize size match, load capacity and manufacture date. If any code is unclear, use manufacturer resources or the DOT decoder link above to confirm. For choosing between acceptable sizes and types, consult the vehicle placard and resources like Choosing the right tire size before fitting replacements.