Tire sidewall numbers explained

Read the main size from left to right

Prefixes and suffixes also matter. A P may identify a P-metric passenger tire. LT identifies a light-truck application. Other regional and specialty markings use different systems. Do not treat two tires as substitutes because the four large numbers look close.

For actual dimensions, open the specification sheet for that exact tire model and size. Look for approved rim-width range, measured rim width, section width, overall diameter, revolutions per mile, load, and inflation notes.

The service description is the number and letter after the size

In 97Y, 97 is the load index and Y is the speed symbol. The load index is a code that maps to a maximum load in a published table. It is not “97 pounds,” and it should not be guessed from the vehicle’s curb weight.

The speed symbol identifies a tested speed capability under specified conditions. It is not permission to drive at that speed, and it does not cancel the effects of damage, age, underinflation, overloading, repairs, or local law.

Some vehicles specify different front and rear sizes, pressures, or load requirements. Some replacement situations also require a particular speed category. The correct answer belongs to the exact vehicle and application.

XL, reinforced, run-flat, and load-range markings describe construction

XL usually means extra load in a passenger-tire system. It does not mean the tire can carry any load at any pressure. The tire’s load table, size, and specified inflation still control what it can support.

Run-flat tires carry their own manufacturer markings and operating limits. Light-truck tires may use load ranges and dual or single load values. These systems are not interchangeable shorthand for “stronger.” Changing construction can also change ride, steering response, weight, required pressure, and emergency behavior.

• Keep the same construction and capability the vehicle requires unless the vehicle and tire makers support the change.
• Do not mix run-flat and conventional tires, or different construction types, without explicit application guidance.
• Check whether the car’s tire-pressure monitoring system and roadside plan still make sense after a change.

The DOT code identifies the tire and shows when it was made

A U.S. DOT Tire Identification Number, often called the TIN, includes plant, size, manufacturer, and production information. On modern tires, the final four digits give the production week and year. 2325 means the 23rd week of 2025.

The complete TIN may appear on only one sidewall, so check both sides. The date is useful when buying, inspecting a spare, checking a recall, or working out how long a car has been sitting on the same tires.

UTQG grades are comparison clues, not a mileage warranty

Many U.S. passenger tires carry Uniform Tire Quality Grading marks for treadwear, traction, and temperature. A line such as Treadwear 300 Traction AA Temperature A is three separate grades.

Use UTQG as one input alongside the tire category, maker data, weather range, vehicle requirement, warranty terms, and reputable testing. Some tire types are exempt or not meaningfully compared by the same shorthand.

Maximum pressure is not the pressure you set every morning

The sidewall lists a maximum load and a corresponding maximum cold inflation pressure for the tire. The vehicle placard lists the pressure chosen by the vehicle manufacturer for the original tire and the car’s loading, ride, and handling requirements.

For normal road use on the specified fitment, use the vehicle placard or owner’s manual. Check pressure when the tires are cold, meaning before driving has added meaningful heat. Do not bleed a warm tire down to the cold specification.

An alternate tire size, a much heavier vehicle setup, towing, track use, or a nonstandard load can require application-specific guidance. Get it from the vehicle maker, tire maker, or a qualified tire professional rather than copying another owner’s number.

Directional, inside, outside, M+S, and mountain-snowflake markings affect use

A directional tire has an arrow showing its intended rotation. An asymmetric tire may mark one side outside and the other inside. A correctly mounted directional tire can still be on the wrong corner if it rotates backward.

M+S, M/S, or similar lettering identifies a mud-and-snow tread designation. The three-peak mountain snowflake symbol identifies a tire that meets a prescribed performance test for severe snow conditions. Neither marking makes worn tread, wrong pressure, or poor judgment disappear.

You may also find manufacturer-specific acoustic, original-equipment, sealant, electric-vehicle, or homologation marks. Look them up in that tire maker’s documentation. A familiar logo with an unfamiliar suffix is not safe to dismiss as cosmetic.

Before buying, record the whole line

• Exact tire brand, model, size, service description, and construction mark

• Vehicle year, model, trim, axle position, load requirement, and original placard information

• Wheel width and diameter, plus the tire maker’s approved rim-width range

• Actual section width and overall diameter from the manufacturer’s specification sheet

• Weather category, direction or side marking, run-flat requirement, and any original-equipment specification

• DOT date code, visible condition, recall status, and the installer’s mounting and pressure plan

The sidewall can tell you what the tire is. It cannot confirm wheel clearance, brake clearance, condition inside the casing, or compatibility with a modified car. Those checks still need the exact parts and vehicle.