How to Match Tire Load Range to Your Towing Needs

Why load range matters for towing

When you tow, each tire carries more weight than it does in everyday driving. The vehicle's gross vehicle weight rating (GVWR) and each axle's gross axle weight rating (GAWR) define the maximum loaded weight. Federal standards require that the sum of the maximum load ratings of all tires on an axle be at least the GAWR. This rule appears in Federal Motor Vehicle Safety Standard 571.110 for vehicles up to 10,000 pounds GVWR and in Standard 571.120 for heavier vehicles.

The load range letter on a tire sidewall indicates its strength at a given inflation pressure. Choosing a tire with too low a load range risks overloading, which can lead to heat buildup, sidewall damage, or failure. Matching the load range to your towing needs is not guesswork: it is a calculation based on the vehicle's certified weight limits and the actual load you place on each tire. For more on how to read those markings, see tire sidewall markings.

Load range letters and ply ratings

Tires are marked with letters such as B, C, D, E, or F. These letters historically corresponded to the number of plies in the tire carcass, a rating called ply rating. Modern tires use fewer plies with stronger materials, so the letter now represents a strength level rather than an actual ply count. Learn more about tire construction types. The U.S. tire industry standards, maintained by organizations like the Tire and Rim Association, define the load and inflation tables that tie each load range to a maximum load rating.

The federal standards define load rating as "the maximum load a tire is rated to carry for a given inflation pressure." This definition appears in Standard 571.109 and Standard 571.139. For light truck tires, the load range letter is part of the service description. You must always refer to the tire's sidewall for the exact maximum load rating and the corresponding inflation pressure. Do not assume that a higher letter automatically fits your rim or vehicle; the tire must match the wheel and the vehicle's load requirements.

Find your vehicle's weight limits

Start with the vehicle's certification label, usually on the driver's side door jamb. It lists the GVWR and the GAWR for the front and rear axles. These numbers are the absolute maximum loaded weights for the vehicle. The federal regulation defines "vehicle maximum load on the tire" as distributing the maximum loaded vehicle weight to each axle and dividing by two. You must ensure that the tire's maximum load rating is not less than that computed per-tire load.

For vehicles with a GVWR over 10,000 pounds, the same principle applies: the sum of the maximum load ratings of tires on an axle must be at least the GAWR. If you plan to add a weight-distributing hitch, remember that it shifts load between axles; still, neither axle's GAWR should be exceeded. Always use the lowest GAWR shown on the label if multiple values appear for the same axle. Understand how load index and inflation work together in tire load index rating.

Calculate the load including trailer tongue weight

When towing, the trailer's tongue weight presses down on the hitch and directly loads the rear axle (or both axles if using a weight-distributing hitch). Add this to the cargo and occupants already in the tow vehicle, then compare the resulting per-axle load to the GAWR. For example, if your rear GAWR is 6,000 pounds and the tongue weight pushes the rear axle load to 5,200 pounds, you need tires whose combined maximum load rating on that axle is at least 5,200 pounds.

For trailers themselves, the trailer's GVWR includes the total weight of the trailer and its cargo. The trailer tires should have a combined load rating that meets or exceeds the trailer's GVWR when divided by the number of tires. Federal regulations allow trailers to use ST tires that meet the requirements of Standard 571.119. Always check the trailer's certification label for its GVWR and match the tire load range accordingly.

Choose the right tire for your towing setup

After you know the maximum load on each axle, select a tire that offers a high enough maximum load rating at the pressure you will run. For light towing with a typical passenger car or SUV, a standard load tire may be sufficient if its load rating covers the axle load. For heavier towing, a light truck tire with a higher load range (such as E or F) is often necessary. These tires have stronger sidewalls and are designed for heavier loads, as defined in the federal standards.

Do not rely solely on the load range letter; compare the actual load rating on the sidewall. That rating is only valid at the corresponding inflation pressure. For towing, you may need to increase the rear tire pressure beyond the normal placard value, but never exceed the maximum molded on the sidewall. Also consider the reduced load rating required when a passenger car tire is installed on a truck or multipurpose vehicle: the tire's load rating must be divided by 1.10 before summing for the axle. For a direct recommendation, see the best trailer tires guide or the best all-terrain tires if you need off-road towing capability.

Finally, keep a safety margin. Federal rules require that the sum of the tire maximum load ratings meet the GAWR, but that is a minimum. Many trailer and towing experts suggest using a tire with a maximum load rating at least 15 percent above the calculated load to account for load transfer, tire pressure loss, and uneven loading. This is advice, not a regulation, but it can prevent overloading at the edge of the tire's limit.

What to pick for your towing use

Questions

What do load range letters like B and F mean on a tire?

Load range letters indicate the tire's strength rating relative to its load capacity at a given inflation pressure. They historically corresponded to ply rating, but modern tires use fewer plies with stronger materials. The letter itself does not give a specific load number; you must read the maximum load rating on the sidewall.

How do I know the GVWR and GAWR of my tow vehicle?

They are printed on the vehicle's certification label, usually on the driver's side door jamb. The GVWR is the maximum loaded vehicle weight, and each axle has its own GAWR. Federal standards require the tire load ratings on an axle to cover at least the GAWR.

Can I use passenger car tires for towing?

Yes, if the tire's load rating at the recommended pressure is enough for the axle load. However, when a passenger car tire is installed on a truck or multipurpose vehicle, the load rating must be divided by 1.10 before comparing to the GAWR. For heavy towing, light truck tires are usually a better choice.

What is the difference between trailer tires (ST) and light truck (LT) tires for towing?

ST tires are designed for trailer axles and are rated for constant highway speeds under load. LT tires are for tow vehicles and can handle a mix of loaded and unloaded driving. The federal standards allow trailers to use ST tires that meet specific requirements. Match the tire to the axle application.

Should I increase tire pressure when towing?

You may need to increase the rear tire pressure to the recommended value for heavy loads, as shown on the vehicle's placard or in the owner's manual. Never exceed the maximum pressure printed on the tire sidewall. Higher pressure increases load capacity but also changes ride quality.