Ram 2500 Tire Load Index: How to Find the Required Rating

The short answer

Replacement tires need a load index equal to or higher than the tires Ram fitted at the factory, and they must reach that capacity at the cold inflation pressure on the vehicle placard. The fastest way to find the original rating is to read the service description on a factory tire. It follows the tire size and has one or two numbers followed by a speed letter. On a light truck tire the format looks like 123/120R. That example only illustrates the format and is not a figure for your truck. The first number is the load index for single-wheel use, the second is for dual-wheel use, and the letter is the speed rating.

If the original tires are gone, use the labels on the driver's door jamb. The Tire and Loading Information placard gives the original tire size and the recommended cold pressures for the front and rear axles. The safety certification label gives the gross axle weight rating (GAWR) for each axle. Divide each GAWR by two to get the minimum weight each tire on that axle must support. A suitable tire's rated capacity at the placard pressure must meet or exceed that number. The maximum load in pounds is also molded into the sidewall, which makes the comparison easy.

How load index and inflation work together

A load index is a code number. It corresponds to a maximum load in a standardized chart. A higher number means more capacity, and each step up is a modest increase. In that chart, an index of 120 corresponds to 3,086 pounds and 123 to 3,415 pounds. The rated figure is the most the tire can carry at its maximum rated inflation. It is not what the tire carries at whatever pressure happens to be in it.

Light truck tires show two numbers because tires mounted side by side on a dual rear axle share the load and are rated lower. The Ram 2500 uses single rear wheels, so the first, higher number applies on both axles. The load range letter, such as E, is a separate marking. It describes how much pressure the casing is built to hold, and you should not read it as the load index. Capacity falls as pressure drops, following load and inflation tables published by tire manufacturers. Running a heavy-duty tire soft for a smoother ride therefore lowers the weight it can safely carry and adds heat buildup.

What changes the answer for your truck

Several configuration details change the specification. These include the model year and generation, cab and bed configuration, engine choice and wheel diameter. A diesel engine adds weight over the front axle, so front axle ratings and tire requirements can differ from a gas-powered truck. Packages such as the Power Wagon and other off-road trims use their own tire sizes. Two Ram 2500s from the same model year can have different requirements, so the labels on your own truck settle the question, not a generic list.

The tire type and size also matter. Passenger P-metric tires are generally a poor fit for a three-quarter-ton truck. When fitted to a light truck, their rated capacity is reduced, commonly by dividing it by 1.1, which usually leaves them short of what the axles need. Changing the tire size for a lift or a different wheel changes the capacity available at a given pressure. A bigger tire does not automatically carry more and may need a different pressure from the one on the placard. Recheck any non-original size against the axle ratings. The speed rating should also be at least equal to the original.

Towing a fifth-wheel or gooseneck trailer, carrying a slide-in camper or running a plow puts heavy loads on one axle. Those loads must stay within the GAWR no matter how strong the tires are, because a higher load index does not raise the truck's own ratings. On four-wheel-drive models, drivetrain compatibility also matters. Fit all four tires in the same size, construction and similar tread depth, because mismatched rolling diameters can strain the transfer case and axles.

Checking a replacement tire step by step

Start by photographing both door-jamb labels and the sidewall of an original tire. Write down the tire size, load index, load range, speed rating and the front and rear placard pressures. For each tire you consider, confirm four things. It is the same size or an approved alternative. Its single-wheel load index is at least the original. Its load range supports the placard pressure. Its speed rating is at least the original. Finally, compare the maximum load in pounds with half of each axle rating, using the capacity at the pressure you will actually run.

After installation, set the cold pressure to the placard figures, not the maximum printed on the sidewall. If the owner's manual gives separate guidance for heavy loads or towing, follow it. Check pressure with the tires cold and again after loading the truck for a trip. Watch tread depth and wear patterns. Uneven shoulder or center wear can point to pressure that doesn't suit the load. Keep a record of the original specification for future tire purchases.

Limits and when to get help

This method shows how to find and verify the rating, but it cannot give the correct index for every Ram 2500 because the requirement varies by build. Get the specification for your VIN from a Ram dealer or a qualified tire shop in any of these cases: the labels are missing or unreadable, the tires on the truck don't match the placard, or the truck has a lift, aftermarket wheels or a nonstandard tire size. They can check the manufacturer's load and inflation tables for the exact tire. Aftermarket wheels carry their own load ratings, which must also cover the axle weights.

Never fit tires with a lower load index than the originals, and never load the truck beyond its axle ratings. If you can't confirm that an alternative size or tire type is adequate, choose a tire that matches the original size, load index and speed rating exactly.