The ultimate use of pusher and tag axles are the Super 16 and Super 18 dump trucks, which have 16 and 18 wheels, respectively. "These trucks are not as complex as you may think," says Cantwell. "There is a specific wheelbase that makes these work, as well as certain axle spacings that are determined by the body companies based on the capacity allowed."
The use of lightweight components can further increase payload. "A contractor spec'ing a Super 16/18 dump truck can maximize the payload by spec'ing lightweight components, such as frame rails, crossmembers, lift axles, aluminum wheels and more," says Reed. "Talking to a body builder can also help determine how the body's center of gravity affects axle loading."
There are also different drive axle variations to consider for special applications. "Later this year, we are going to be introducing a tridem axle - a tri-drive rear axle," says Ginter. "Tridem axles provide more traction than a conventional tandem axle, but their use does not change the gross vehicle weight restrictions compared to the conventional tandem in some regions."
With so many choices, it can be intimidating to properly spec a truck. Your dealer is the best place to start since it can assist with the necessary calculations.
"Our order spec'ing tool that the dealers use has all the calculations in it to assist the dealer. But knowing how to do it manually always helps for checking," says Cantwell. "Multi-axle trucks are much harder. You need to figure the weights with the axles up and down, plus space everything to the limitations of the lift axles, as well as limitations different states put on lift axles."