So you were driving down the highway the other day and found yourself behind a pickup truck that looked a bit…odd. You counted and it had one, two, three, four rear tires! Why build a truck that’s thicc with two Cs? Put simply, more rear tires equal more payload capacity.

How much weight can a tire carry?

Every tire has a tested load index. For modern radial tires, this can be over a ton–for each tire. Think about it, some light-duty pickup trucks with just four tires boast a GVWR of 8,000+ pounds.

That said, there is an upper limit to how much weight each tire can support. And the faster you plan to drive, the less weight you can put on each tire. In addition, some municipalities attempting to preserve their roads limit how much weight you can place on each tire.

With some heavy-duty pickup truck towing capacities above 18,000 pounds, two rear tires won’t cut it. For this reason, all of the Detroit Three offer heavy-duty trucks with dual rear tires.

Curious about the weight a single tire can support? Read more about how automakers choose and rate tire load indexes.

What are pickup trucks with four rear tires called?

To get a pickup truck with four rear tires, you have to order the dual rear wheel setup. Most pickup truck fans call these heavy-duty rigs “duallys.”

You can’t order a full-size, light-duty truck with dual rear wheels (think F-150 or the equivalent). But you can get dual rear wheels on the heaviest-duty trucks offered by the Detroit Three. This includes the Ford Super Duty series, the Ram 3500 and up, and General Motors’ mechanically identical Chevrolet Silverado 3500 and GMC Sierra 3500.

Are there any downsides to dual rear tires?

There are several reasons you might want to think twice about buying a heavy-duty truck with dual rear tires. The most common concern is the higher upfront cost and higher maintenance cost of a “dually” truck.

Most automakers will charge you at least $2,000 extra to assemble your heavy-duty truck with dual rear tires. This dually truck has a regular rear axle and brakes, but it has four rims and four rear tires. It also has specially designed, wider rear fenders. All of these components cost the automaker money.

You also have to consider the cost of replacing these tires. When your tires are finally bald, you can’t get away with ordering just four, you’ll need a set of six tires. If you live in a snowy state and want to invest in separate winter tires, you’ll be paying extra for this set too.

A dually truck is also wider than a regular truck. The difference is not too extreme. But if you do a lot of off-roading on narrow trails or sliding into tight parking spaces, you might want to reconsider ordering a dually truck.

Finally, there are rare instances where you will have to pay a higher toll for your “commercial grade” truck with its dual rear wheels. In most cases, you’ll only pay the two axle toll–but not always. There are even a couple parkways through residential neighborhoods that do not allow “commercial grade” trucks with dual rear axles.

Next, find out why some pickup trucks have a locking box in their bed.