Much of the decision has to do with the steels used in construction. "With the advent of the higher strength steels, you get the strength you need and you really don't need crossmembers," says Paulsen. "The way we explain it to our customers is that all crossmembers are going to do is create opportunities for your floor to washboard, which will mean you are not going to have the clean-out that you want.'
The new higher strength steels are flexible. "They will flex and spring back," says Paulsen. "We actually have cases where using high-strength steel and crossmembers worked against each other. If you use it with a cross member, it will actually flex and stay deformed."
In some traditional rectangular bodies made of milder steel, crossmembers still have a useful purpose. "If you are trying to lighten the floor because you are not hauling demolition, maybe it is still an advantage to go with crossmembers," says Pick.
Miller adds, "If the floor in a body is made of milder material, added crossmembers are necessary to keep the floor from washboarding."
Some manufacturers have converted their customers to bodies without crossmembers. "We have virtually eliminated the crossmembered body," says Pick. "We offer them, but we don't sell very many of them."
It is important to realize that all metals will eventually deform to some degree. "All material will deform and deflect at some point," says Paulsen. If you have longitudinal supports with no crossmembers, that is not a problem. "You end up with a series of chutes." The material still flows out the back of the bed without getting hung up.
Select the right front-end design
The front of the box is typically available in a straight configuration with a doghouse for the hoist cylinder, a straight configuration with a bailmount front hoist and a sloped front. Often, the choice has to do with local bridge regulations.
"If you go to the Eastern states, you want to get more weight to the front axle," says Paulsen. You want the body as close to the cab as possible, which favors a straight front. "The bailmount, if it works with your weight distribution, eliminates the doghouse. It eliminates a corner where the material can get caught."
The box remains free of obstructions. "A bailmount hoist eliminates the doghouse altogether, keeping the hoist cylinder in front of the body," says Miller.
Sloped fronts have recently become a popular option. "A sloped front provides the opportunity to reduce the doghouse space needed for the hoist," says Pick. This allows more aggregate in the body. "Then, you also have less of a worry as far as that doghouse area filling up during cold weather because you have extra bends and extra nooks."
Sloped fronts also offer some of the same advantages as the elliptical body shapes. "They use the sloped front if they are hauling big rock so they don't beat up the doghouse," says Gettis.
The straight front requires a substantial space for the hoist. "A straight front requires a larger cut-out for the doghouse," says Miller. "The greater the size of the doghouse, the greater the reduction of payload capacity."
Match to your application
The reason so many choices exist is that no dump box is perfect for every application.
"Pretty much everyone is trying to put out a decent quality product," says Pick. "You just have to make sure that you are getting a match for what you are hauling."
Paving contractor finds a match
Mundall Trucking is a family-run asphalt-hauling firm in the Phoenix, AZ, market. The company operates seven-axle Superdumps that scale 25.7 tons of material in the morning, full of fuel, with the driver inside. The 80,000-pound gross weight trucks have a 20,000-pound-capacity set-forward steer axle, three 8,000-pound steerable pushers, 46,000-pound tandem drives and a Strong Arm trailing axle.
Mundall found a good match for its Superdump chassis and axle with a lightweight, high-strength steel bed with aluminum tailgate made by Strong Industries. The Superdump bed offers three distinct characteristics: a conical, elliptical shape that gradually becomes wider toward the rear of the bed; an extended floor that eliminates the need for an asphalt apron; and a low tare weight.
Most dump beds are basically the same shape at either end. In transit, the material becomes compacted and it comes out of the bed in uneven layers. The Superdump bed has an elliptical-shaped floor and conical-shaped sidewalls that become wider toward the rear. The shape lets the payload loosen up as it flows from the bed, as if it is being poured out of the large end of a funnel.