Long before a single load is booked or any wheels turn, someone - usually a fleet manager - needs to determine exactly what is going to separate the road and the load. There's a lot riding on this decision because, as much as some would like to think otherwise, a trailer is never just a trailer. It can be manufactured to many different specifications, with multiple raw material options, dozens of load and geographical considerations, various top speed requirements and hundreds of possible axle configurations coming into play. And it all comes down to one objective - the ideal trailer for an operation's specific loads.
To select the right trailer, the one that will require the least amount of maintenance, provide the greatest lifespan and deliver the highest possible return on investment, it is vital to understand the most important factor of all - capacity.
50 Tons in the Making
There are five contributors to capacity ratings. They apply to any kind of open trailer, from flat and step decks to lowbeds, and each can be varied to meet a carrier's specifications.
It begins, of course, with the materials used to build the trailer, specifically their sizes and weights. From there, capacity encompasses the overall weight that a trailer can carry, the area of the deck in which it can carry that weight, the speed at which the trailer will generally travel and the safety factor.
To make an apples-to-apples comparison, consider one 50-ton lowbed alongside another 50-ton lowbed. Because, just as a trailer is never just a trailer, not all 50-ton lowbeds are created equal.
Load Concentration: Half Deck, Full Utilization
There are more than 50 manufacturers of lowbed heavy-haul trailers in North America, and they apply several methods of rating the capacity of their trailers. Since there is no industry-set or government-mandated system, it's up to every buyer to be in tune with the method each manufacturer uses before making a purchase decision.
A key difference between manufacturers' ratings comes in load concentration, or the length of the deck that can handle the rated weight. Obviously, a 26-foot, 50-ton lowbed can haul 50 tons. But how much of the deck those 50 tons occupy is just as important as the weight itself. Whereas one trailer might need the entire length of the deck to be rated at 50 tons, another can be rated for 50 tons in a 16-foot span, and another can handle that same weight in half the deck length.
For example, a 26-foot, 50-ton lowbed might be rated for the trailer's entire span with equal weight distribution. In that case, the trailer would need to be hauling materials that run the entire length of the trailer, such as long steel poles, lumber or concrete culvert sections.
However, if the payload is a 100,000-pound excavator that's only 13 feet long, a trailer rated for the entire deck length, or even for 16 feet, won't be right for the load. Even though the load is only 50 tons, that trailer will be overloaded because the weight will not span the entire length of the deck; making it too concentrated for the area the excavator covers. For a trailer that's rated at full deck length or 16 feet to safely handle the excavator, it would likely need to be rated at 55 or 60 tons.
So again, using the 13-foot, 100,000-pound excavator as the payload, the ideal trailer will be one rated at half the deck length. Trailers rated for half the deck length can carry a specified load in just that, half the length of the deck. These ratings give a more realistic indication of the concentrated loads the trailer will be able to handle safely and without structural failure. In addition, manufacturers who build trailers with half-deck ratings often do so with a two-point rigid load base specifically for the tire spacing, or hot spots, of large equipment and heavy machinery.
Load Distribution: Scaling Out
How a load is distributed over the deck and the axles can be just as important as the overall weight rating. However, even though the trailers will be operating in the United States, the states are not very united when it comes to axle weight laws and regulations.
All across the country, the laws and regulations related to weight change from state to state. Companies operating in Indiana deal with one set of laws and regulations, but when they cross the border into Ohio they run into entirely different set of regulations. Pennsylvania has yet another distinct collection of rules of the road and so on along the truck's route.
Fleet managers need to be aware of, and plan for, variances between states and regions where their trailers will be used. It's important to have the proper trailer configuration to make the load distribution work for a fleet's particular area of operation. Manufacturers bear some responsibility, too, and should work with buyers to define not just the best trailer for the cargo those buyers will be carrying, but also the best axle configurations for maximizing the load in every one of the states they'll be hauling through.
Clearly, it's impossible to max out a trailer's capacity in every state, but the goal of most interstate heavy-haul carriers is to get a trailer as close to the maximum as possible across all the states where the carrier intends to operate.
There are many ways to achieve the best possible weight distribution over the axles. It may be as simple as adding a fourth flip axle or as complicated as adding two or three axles and spreading them apart to make sure they can each accept an equal amount of weight from the payload. And there are other possibilities in between depending on the specific state's regulations and the nature of the load.
For example, carriers can vary gooseneck lengths in the front to achieve the proper steer weight and drive axle weight. Carriers also can alter the distances between axles and axle groups to hit max weights and remain in compliance with various state laws. With an East Coast trailer, for example, they can add shims to a rigid spread bar or, if the trailer has a nitro version of a spreader bar, use hydraulics to vary the weight distribution. Yet another way is to move the load closer to one end or the other to properly distribute weight over the axles. And, finally, a carrier can use a jeep dolly to add extra axles, thereby lowering the per-axle weight distribution.