RV Tire Load Range: What Letter Do You Need?

Understanding load range letters

Load range letters, such as B, C, D, E, and F, originally indicated the number of plies in a tire's construction. Today they primarily correlate with maximum permissible inflation pressure and load carrying capability. Under Federal Motor Vehicle Safety Standard No. 109, the load rating is defined as the maximum load a tire is rated to carry for a given inflation pressure, and the maximum load rating is the rating at the tire's maximum permissible inflation pressure.

For RVs, you will typically see ST (special trailer) tires on travel trailers and fifth wheels, and LT (light truck) or larger commercial tires on motorhomes. The load range letter you need depends on the weight you are carrying. A higher letter generally means a higher load capacity at a higher inflation pressure, but you should never select a tire based on the letter alone. Always compare the tire's actual load rating printed on the sidewall to the load your axle imposes.

If you are deciding between load ranges, the comparison matters more than the letter. For example, a load range C tire may be sufficient for a lightly loaded trailer, while a load range E tire might be required for a heavier fifth wheel. The right choice is always the one that meets the axle-load rule described in the next section. See our guide on tire load range C vs E and tire load range for towing for more context.

How to find the load range your RV needs

Your RV's certification label, usually located on the driver's side door frame or near the hitch, lists the gross vehicle weight rating (GVWR) and the gross axle weight rating (GAWR) for each axle. Federal regulations require that the sum of the maximum load ratings of all tires on an axle must be at least that axle's GAWR. For vehicles with a GVWR of 10,000 pounds or less, this rule is set by FMVSS 110. For heavier vehicles, FMVSS 120 applies the same principle.

To determine the required load range for your RV, follow these steps:

1. Weigh your RV when fully loaded for a trip (including water, fuel, cargo, and passengers). Use a certified scale to get the actual weight per axle. 2. Read the GAWR from the certification label. The axle weight should not exceed this value. 3. Check the sidewall of each tire for its load range and maximum load rating (at a specified inflation pressure). 4. Add up the maximum load ratings for all tires on one axle. The sum must be equal to or greater than the GAWR. 5. If the sum is below the GAWR, you need a tire with a higher load range or a higher load rating at an acceptable pressure.

This calculation is the only correct way to know which load range you need. The letter alone does not guarantee adequacy because tires of the same load range can differ in their actual load ratings depending on size and rim width. Refer to our tire load capacity chart and tire vehicle load inflation for more details on how load ratings vary with pressure.

Matching tires to each axle load

The axle-load rule is straightforward: for each axle, the sum of the maximum load ratings of the tires on that axle must be at least the GAWR. For a single axle with two tires, each tire must contribute half of the required capacity, but the rule is applied at the axle level. For dual wheels (two tires on each side), the sum of all four tires must still meet the GAWR.

If you plan to increase the load capacity of your RV, either by adding cargo or changing the vehicle's configuration, recalculate the axle loads and verify that your tires still comply. Overloading a tire beyond its rated capacity can lead to heat buildup, tread separation, and blowouts, particularly at highway speeds. The purpose of the federal tire selection standards is explicitly to prevent tire overloading, as stated in FMVSS 110.

Remember that a tire's load rating is only valid at the corresponding inflation pressure shown on the sidewall. Lowering the pressure reduces the load capacity. Never exceed the maximum permissible inflation pressure printed on the tire. For guidance on adjusting pressures for heavy loads, see our article on tire pressure basics and tire inflation pressure chart.

Why overloading happens

Overloading is more common than most RV owners realize. The most frequent causes are underestimating the loaded weight of the RV, adding heavy accessories (such as generators, batteries, or water tanks) without recalculating axle loads, and assuming that a higher load range letter automatically makes a tire suitable for any load. Another factor is that travel trailers and fifth wheels often use ST tires, which have load ratings specifically defined for trailer service under FMVSS 119.

RV tires are also subjected to sustained highway speeds and high ambient temperatures, which increase internal heat. A tire that is close to its load limit can overheat and fail even if the static weight is within the rated value. Inflation pressure must be checked when the tires are cold, as per FMVSS 138 requirements for tire pressure monitoring systems on lighter vehicles, and adjusted for the actual load.

Finally, many RV owners upgrade to larger tires or wheels without verifying that the new tires' load ratings are appropriate for the existing axles. The correct approach is to always compute the sum of maximum load ratings and compare it to the GAWR, regardless of the tire's load range letter. For signs of overloading, review our article on tire overload damage signs.

Load range advice for motorhomes, travel trailers, and fifth wheels

Motorhomes, especially Class A and Class C, often have heavy front and rear axles. They typically use LT (light truck) tires or larger commercial tires. The load range you need depends on the GAWR of each axle; many motorhome owners find that load range E or F is necessary, but the only way to be sure is to run the calculation. If you are shopping for new tires, browse our best light truck tires guide to see options with appropriate load ratings.

Travel trailers and fifth wheels are usually equipped with ST (special trailer) tires, which are designed specifically for trailer service. These tires have their own load range designations and are tested under FMVSS 119. For a travel trailer with two axles, each axle's GAWR is typically lower than the total GVWR, but you still need to match the sum of the tire ratings to each axle. Many trailers use load range D or E tires, but again, the exact requirement comes from your axle weights. See our best trailer tires guide for a range of options.

Fifth wheels have added complexity because a significant portion of the load transfers to the truck's rear axle. The trailer's own axles still have GAWR limits, and you must also ensure that the truck's tires can handle the additional pin weight. For the trailer itself, the same axle-load rule applies. If you need higher load capacity on a 17.5-inch wheel, check our best 17.5 inch tires guide. For a 16-inch wheel setup, compare the ratings in our best 16 inch tires guide.

Always remember that the load range letter is only a starting point. The actual load rating on the sidewall at the specified pressure is what matters. If you are uncertain, err on the side of a higher load range or a larger tire, and verify that the tire is listed for use on your RV's rim size. See our article on tire load range for RV for a summary of this topic.

What to pick for your use

Questions

What is the difference between load range C and load range E?

Load range E tires are generally rated for higher maximum inflation pressures and can carry more load than load range C tires at those pressures. The exact difference varies by tire size and construction, so you must compare the sidewall load ratings rather than depend on the letter alone.

Can I use a higher load range tire than required?

Yes, you can install a tire with a higher load range than the minimum needed, as long as the wheel rim is approved for that tire and the tire's maximum inflation pressure does not exceed the rim's rated capability. It provides a safety margin, but you should still inflate to the pressure recommended for the actual load.

How do I find the gross axle weight rating (GAWR) of my RV?

The GAWR is printed on the certification label, typically located on the driver's side door frame, the door pillar, or near the hitch for trailers. It lists the maximum weight each axle is rated to carry as specified by the manufacturer.

Do ST trailer tires have different load ratings than LT tires?

ST tires are designed specifically for trailer service and are tested under FMVSS 119, while LT tires are intended for trucks and may have different load and speed capabilities. ST tires often have higher load ratings for a given size, but you must always verify the actual sidewall rating for the specific tire.

What happens if my tire's load rating is lower than the GAWR?

If the sum of the maximum load ratings of the tires on an axle is less than the axle's GAWR, the tires are overloaded. This can cause excessive heat, tread separation, and blowouts. You must replace them with tires that provide sufficient load capacity or reduce the weight on the axle.

Can I increase load capacity by raising tire pressure?

A tire's load rating at a given inflation pressure is determined by the manufacturer. You can use the pressure that corresponds to the required load rating, but you cannot exceed the maximum permissible inflation pressure printed on the sidewall. Increasing pressure beyond that does not increase load capacity and may be dangerous.