Ask dump truck operators what matters most to their bottom line and nine out of 10 will say, “Payload, payload, payload.” When you’re billing by weight, and you’re hired because you can haul more than the next guy, it’s a reasonable response.

But with straight dump trucks, payload is only one part of the productivity equation. Yeah, you want to move as much rock, dirt, asphalt, or whatever as you can. But you really want to do the job in the fewest number of trips possible. That means maximizing what you can legally haul and then getting the material out of the bed quickly, efficiently, and cleanly, with minimal manual labour.

Dump bodies come in a variety of shapes and sizes, and like any other piece of equipment you spec, your best choice will hinge on the cargo and gross weights you plan to haul. The bed not only carries the load and takes a pounding, it also helps distribute weight as evenly as possible across all axles.

It’s as big a job as there is, and one reason why more truck manufacturers are packaging their chassis with a selection of pusher axles, bodies, and hoist equipment. The cooperative engineering helps them create a more productive, efficiently assembled chassis-body combination-not to mention one they can deliver faster. You can spec a complete dump truck and administer warranty through the dealer, a convenient one-stop shopping arrangement.

“The average dump bed company builds the bed to the nearest inch, they use the same latches and components they had 20 years ago, and they create the same challenges to the truck manufacturer and to the customer,” says Brooks Strong, president of Strong Industries, a manufacturer of dump bodies and trailing axles in Houston, Texas. “Yet contractors who hire dump truck operators are more demanding in terms of productivity, safety, and reliability. The truck operators who will get the first call in the morning are the ones who help the contractor make money.”

When you’re looking at a dump body, the most basic point of comparison is how much material it can hold. Like any open-topped container, a body’s length, width, and the height of its sides and tailgate determine its volume (described in cubic yards).

But bigger isn’t necessarily better. It’s not how much volume you have that makes the difference. It’s how you use it.

Most dump boxes in Canada will be made of steel (combining durability with economy) and have vertical or slightly sloping sides and a flat bottom. It’s ideal for general hauling because it’s so versatile: you can take tree stumps today, concrete or rock tomorrow, and topsoil the day after that. The deep corners add to the volume of material the bed can carry, and the flat bottom does the best job of spreading. If your jobsite is a gravel driveway, you can chain the tailgate to restrict the opening, raise the bed to 30 degrees, and confidently lay down a nice, even layer of material.
But there are drawbacks to being boxy.

Structurally, the basic box takes little effort to twist, so manufacturers add vertical and horizontal structural reinforcements (imagine the sight of a dump box wobbling around on its hoist). The constant pounding of material being loaded into the bed can cause the steel between the crossmembers to cave, resulting in a washboard effect on the floor and sides. You can try to prevent this by adding more bracing, but the extra weight will come at the expense of payload.

The box shape does little to distribute weight where you need it, and it will hold on to material where you want it least.

A square bed has corners and probably a doghouse for the hoist, and no one wants to have to climb into the bed and scrape up the clods of dirt or mud that accumulate there. Even in a body plumbed to radiate the heat of the truck’s exhaust, if the material is wet, it may freeze in such a way that the load becomes unbalanced, raising the potential for a tip-over. And there’s not a tailgate on the market that can stand up to a block of ice and mud the size and weight of a Volkswagen barreling through it.

A rounded bed is lighter, less expensive to build, and more difficult to dent because the shape of the bed is a structural member itself. The curved “bathtub” shape is simply more effective at handling glancing blows of rough cargo like concrete debris and rocks.

But the sloping sides tend to force loose cargo downward and concentrate it toward the centre of the bed. That’s fine for hauling asphalt, where you have the conveyer in the centre of the paver. But probably not for spreading gravel or handling general construction work.

Most beds are basically the same shape at both ends. As the material moves toward the tailgate, it compresses and peals around the corners, literally wearing away metal as it goes out the back four feet of the bed.

An elliptical bed has a radius-shaped floor that gets bigger toward the rear, so the material spreads out and loosens up as it leaves the bed. It’s ideal for a load like asphalt: the driver doesn’t have to raise the hoist as high to get the load to break, and the asphalt flows more easily, quickly, and consistently into the paving machine.

If you want to invest in speed–and save some wear and tear on your aluminum or steel bed–consider a top-quality bed liner. There are many different liners on the market, and the most common ones are made of various industrial-grade polymers, the sort of stuff that won’t wilt in the heat of asphalt or get pummeled into submission by a load of aggregate.

The need for a quick turnaround is why you’re running a straight dump instead of a transfer trailer, after all. With a single unit, you’re into the job site, you raise your bed until the load breaks, and then get out of the gate.

If your driver has to spend 30 minutes cleaning material out of the corners of the bed, or has to stop and manually spread a line of gravel across a driveway, you’re losing productive time. Maybe a load a day. In a competitive market, it’s time you can’t afford to dribble away.