How to Read a Tire Sidewall: Size, Load Index and Speed Rating

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Every tire carries the information you need to buy a matching replacement right on its sidewall. Once you know how to read it, you can compare tires confidently. This guide breaks down a typical light truck tire marking piece by piece.

A worked example

Take the marking LT275/65R18 123/120S E. It breaks into these parts:

• LT — light truck tire.
• 275 — section width in millimeters.
• 65 — aspect ratio: the sidewall height is 65 percent of the width.
• R — radial construction.
• 18 — the wheel diameter in inches that the tire fits.
• 123/120 — load index for single and dual use.
• S — speed rating.
• E — load range.

Load index

The load index is a code, not a weight. Each number corresponds to a maximum load per tire at the tire’s maximum pressure; higher numbers carry more. Some LT tires show two numbers separated by a slash: the first applies when the tire is used singly, the second when it is used in a dual (side-by-side) rear pair. Use the tire maker’s load table to convert the code into pounds or kilograms.

Speed rating

The letter after the load index shows the maximum speed the tire is rated for under its rated load. S is 112 mph, T is 118 mph, H is 130 mph. Truck tires are often S, T or R rated. Never go below the speed rating the vehicle maker specifies.

Load range

Load range is a letter that describes the tire’s strength and the pressure at which it reaches its maximum load. C corresponds to a 6-ply rating, D to 8-ply, E to 10-ply and F to 12-ply. A higher letter means a stronger tire with a higher maximum pressure. Our LT vs P-metric guide explains why this matters for towing.

The DOT date code

Look for the letters DOT followed by a string of characters. The last four digits are the week and year of manufacture. A code ending in 2524 means the 25th week of 2024. Tires age even when not used, so check the date when buying and avoid tires that have sat unsold for years.

Other markings

• Maximum load and pressure: printed on the sidewall, usually in both pounds and kilograms.
• M+S or 3PMSF: mud-and-snow marking or the three-peak mountain snowflake symbol for severe snow service.
• Treadwear, traction and temperature: the UTQG ratings, where printed.

Using it to shop

Maximum load and recommended pressure are different things

The pressure printed on the tire’s sidewall is the maximum the tire can take to reach its maximum load; it is not the pressure you should normally run. The placard on the driver’s door jamb lists the pressures the vehicle maker recommends for the original tires. When you tow or carry a heavy load, the tire maker’s load and inflation table shows how much pressure you need for that weight.

Tread depth

New truck tires typically start with deep tread that wears down over time. Most US states set a legal minimum of 2/32 inch. A simple check is to put a penny into a groove with Lincoln’s head pointing down. If you can see the top of his head, the tread is at or near the minimum and the tire needs replacing. Many owners replace sooner for wet and snow traction.

How old is too old

Rubber ages with time, heat and sunlight. Many vehicle and tire makers advise replacing tires about ten years after their date of manufacture, regardless of tread, and having them inspected annually once they are around five years old. A tire with plenty of tread can still be past its safe life.

Spare tires and mixed sizes

Your spare is also a tire, with the same markings and the same aging. Check its date code and its pressure at the same time as the others. If you change to a size different from the factory size, confirm that the spare, if it is a full-size one, still matches or that you carry a suitable replacement.

When replacing tires, match the size, load index and speed rating at minimum, and keep the load range the same or higher. Then check that the tire width suits your wheel. Browse current light truck tires and compare their listed sizes with what you wrote down from your sidewall. If you are changing wheels as well, our 8-lug wheel guide is the place to start.