Tire Load Range vs Load Index: Key Differences for Trucks

Load range letters and ply rating

Load range is a letter code found on light truck tires that indicates the tire's structural strength and its ability to handle inflation pressure. It evolved from the old ply rating system, where a tire's strength was expressed by the number of plies, or layers of rubber-coated cords, in its carcass. The federal definition of ply appears in 49 CFR 571.109, which describes a ply as a layer of rubber-coated parallel cords. Today, radial tires often use fewer, stronger plies, so the letter takes over as a shorthand for the load-carrying capability.

The National Highway Traffic Safety Administration's standards for tires on heavy vehicles, such as 49 CFR 571.119, mention load range when specifying strength test requirements. This shows that load range is a recognized metric in U.S. regulation. Common designations on modern light trucks include C, D, E, and higher, with each step indicating a greater strength and a higher allowable inflation pressure. While the exact load capacities vary by size, the letter gives you a quick way to compare strength across tires from different manufacturers. For more on reading sidewall markings, see tire sidewall markings.

Load index numbers

The load index is a numeric code that appears as part of the tire's service description. For example, in a size like P225/60R16 97H, the 97 is the load index. This number is assigned by international standardization bodies such as the European Tyre and Rim Technical Organization (ETRTO), which publishes tables that match load index numbers to specific load capacities in kilograms or pounds. The load index, combined with the speed rating (the letter after it), forms the service description that appears on the sidewall.

Unlike the load range letter, which groups tires into broad categories, the load index gives a discrete value at a given inflation pressure. Federal regulations define load rating as the maximum load a tire can carry at a given inflation pressure (see 49 CFR 571.109). The load index is one way to express that rating, and it is used on both passenger car tires and light truck tires. When you see a load index, you must also know the corresponding inflation pressure to understand the actual capacity. For deeper insight, check our guide on extra load tires.

Load range vs load index: key differences

The main difference is the format: load range is a letter, load index is a number. Load range is primarily used on light truck (LT) tires and is linked to the tire's strength category and its maximum permissible inflation pressure. Load index appears on nearly all tires, including passenger cars, and provides a precise load capacity at a reference pressure. Both are derived from the same underlying definition of load rating, but they communicate it in different ways.

Here is a side-by-side comparison to help you read tire sidewalls:

How ply rating fits in

Ply rating originated when tire builders added more layers of cord to increase strength. A 6-ply rating meant the casing contained six layers. As materials advanced, manufacturers could achieve the same strength with fewer plies, so the actual number of plies became less meaningful. Load range letters were introduced to standardize this rating across the industry. Modern tires may have a load range E that describes a strength level that would once have required ten plies, but the exact correspondence is not part of any federal definition.

The federal standards still define ply and ply separation in the context of tire construction. For example, 49 CFR 571.139 lists ply separation as a type of failure that must not occur during testing. When you understand that load range is a proxy for the old ply rating, you can see why a higher load range typically means a heavier-duty tire, even if the number of actual plies is lower.

Choosing the right load rating for your truck

The right load rating starts with your vehicle's rated capacity. For vehicles with a gross vehicle weight rating (GVWR) of 10,000 pounds or less, Federal Motor Vehicle Safety Standard 110 (49 CFR 571.110) requires that the sum of the maximum load ratings of the tires on an axle must be at least the gross axle weight rating (GAWR). For vehicles above that weight, Standard 120 (49 CFR 571.120) imposes a similar requirement. Check the placard on your driver's door jamb to find the GAWR, and make sure the tires you choose have a load capacity that meets or exceeds it. See our guide on vehicle load and inflation to understand how to use those numbers.

Beyond the regulation, think about how you actually use the truck. If you regularly tow a heavy trailer or carry a full payload, a higher load range like E or a load index that covers the extra weight is a safer choice. It may ride more firmly because the sidewall is stiffer and requires higher inflation pressure. If your truck is mostly a daily driver, a lower load range might offer a smoother ride while still meeting the placard's requirements. Always use the vehicle manufacturer's recommended cold inflation pressure, not the maximum pressure printed on the sidewall. For more on inflation, see tire inflation pressure chart.

You can also look up the tire's load and inflation tables for exact numbers. Those tables are published by organizations like ETRTO and the Tire and Rim Association, and they list the load capacity at each inflation pressure for a given size and load range. When shopping for replacements, compare the load range and load index of the new tire with the original equipment to ensure you stay within safe limits. Start by reviewing our best light truck tires for options that meet your needs.

What to pick for your use

Questions

What does load range E mean?

Load range E is a letter designation for light truck tires that indicates a higher strength category compared to C or D. It historically corresponded to a 10-ply rating, but today it is more about the tire's maximum permissible inflation pressure and load capacity. The exact load rating depends on the tire size and inflation pressure.

Is a higher load index always better?

Not necessarily. The load index must match your vehicle's weight and usage. A higher load index means the tire can carry more load at a given pressure, but it may also have a stiffer ride. Always meet the minimum required by your vehicle's placard, but you don't need to exceed it for normal use.

Can I use a passenger car tire on a light truck?

You can, but you must reduce the load rating by dividing by 1.10 when calculating the sum for an axle, as required by Federal Motor Vehicle Safety Standard 120. Passenger car tires are not designed for the heavy loads and higher pressures that LT tires handle. For truck use, LT tires are usually the better choice.

Where do I find my vehicle's required load rating?

Check the tire and loading information placard on the driver's side door jamb or the glove box. It lists the original tire size and the recommended cold inflation pressure. The gross axle weight rating (GAWR) is also there; your tire's load rating at that pressure must be at least the GAWR per axle.

Are load range and ply rating the same?

No. Ply rating is a historical term based on the number of cord layers. Load range is a modern letter system that replaced it, representing the tire's strength and pressure capability. The two correlate loosely, but a modern tire with few plies can have a higher load range than an old tire with many plies.