Selecting a trailer is more than comparing the price tag. There are several implications that need careful consideration before signing a check. The most important of these is safety. Safety has a tremendous impact on a trailer's return on investment because of unconsidered costs that can arise if a contractor inadvertently exceeds the trailer's capacity. These costs can be several times more than the trailer's original purchase price. Selecting the right trailer with a focus on safety, maximum efficiency and a high ROI is crucial.
Capacity's Five Points
There are five contributors to capacity ratings. They include the materials' properties used in building the trailer, the area of the deck, safety and the speed at which the trailer will generally travel. These contributors apply to any kind of open trailer, and trailer manufacturers can manipulate their designs according to each rating while meeting a contractor's specifications.
Concentrated Strength
There are more than 50 manufacturers of lowbed heavy-haul trailers in North America, and they apply several different methods of rating the capacity of their trailers. Because there is no industry-set or government-mandated system, it is 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 is 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.
Trailers rated for half the deck length can carry the specified load rating in just 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. 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.
Spreading The Load
How a load is distributed over the deck and the axles can be just as important as the overall weight rating. Although the trailers will be operating in the United States, the states are not very united when it comes to axle weight laws and regulations. Fleet managers need to be aware of variances between states and regions where their trailers will be used. It is important to have the proper trailer configuration to make the load distribution work for a fleet's particular area of operation.
Working with experienced manufacturers helps 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 through which they will be traveling.
Clearly, it's impossible to max out a trailer's capacity in every state, but the goal of most regional contractors is to get a trailer as close to the maximum as possible across all the states in which the contractor intends to operate. Achieving the best possible weight distribution over the axles may be as simple as having a trailer designed to accept a fourth flip axle or as complicated as a trailer configuration with two or three axles and components to distribute an equal amount of weight from the payload.
Up to Speed
Another capacity determinant is speed. While some manufacturers rate their trailers at 55 mph, others rate them at 65 mph. Naturally, the slower a rig travels, the less added weight or stress is placed on the trailer. Though the trailer will still encounter potholes, railroad tracks and other road dynamics, the impact on the trailer is diminished with a lower speed.
Playing it Safe
A trailer's safety rating also comes into play when discussing capacity. Without understanding the safety rating, it's difficult for a contractor to get a clear, comprehensive picture of true capacity.
A safety rating is an indicator of how much stress a trailer can safely handle. A widely accepted average magnification of payload weight on a trailer due to road dynamics is 1.8 to 1 ratio. On average, the stress placed on a 50-ton-rated trailer by a 50-ton load when the rig hits those bumps equals 1.8 times 50 tons, or 90 tons.
Keep in mind that the 1.8 multiplier is only an average. On any given haul, the stress placed on the trailer can go above that level multiple times. If no cushion is built in to the trailer to handle those spikes in stress, there will be more potential for long-term, progressive structural damage.
There is no universally prescribed level for safety ratings, so they vary from manufacturer to manufacturer. They range from a safety factor of 1.8 to 1, which allows for no margin, to an industry high of 2.5 to 1, which is considered an ample cushion for even the most extreme road dynamics.
Not only does the safety rating tell a contractor how strong his trailer is, it's also a good indicator of potential life. The greater the difference between the static design safety factor and the dynamic 1.8 average multiplier, the longer one can expect a trailer's useful life expectancy to be.
A safety rating should never be used to determine how much weight can be added over the capacity rating and still keep the load, the driver and travelers on the road safe. Road dynamics will always increase the stress of the load and the trailer needs to have a margin to accommodate that added stress.
Materials Make the Trailer
Safety factors are strongly related to the quality of the components in the trailer, and that gets down to the fine details of the steel and the deck material. Manufacturers have several options when choosing steel. For the most capacity and smallest impact on the trailer weight, some manufacturers use a T1 material with 100,000 psi minimum yield. T1 not only has maximum strength versus ductility, but also equates to a lighter, stronger trailer frame over other materials. A trailer's decking is continually exposed to the elements, making durable decking with a long wear life also crucial. Apitong decking provides a tougher, longer lasting wood in comparison to other varieties, such as oak or pine. Tightly woven and incredibly dense, Apitong is less susceptible to chipping and cracking, and provides more traction than a smooth metal surface.
Overload Risk
Sometimes trailer owners or operators don't completely understand the capacity rating and mistakenly put more weight on the trailer than it is built to handle, or more weight in a concentrated area than it can handle. When a trailer breaks, the manufacturer hears about it.
Often, the complaint will be that a 50-ton trailer broke when it was hauling less than a full payload. The reason is not in that 40-ton load, but the number of times the trailer previously was overloaded and by how much each overload exceeded the yield strength of the trailer's load-bearing beams and cross members.
Yield strength refers to the amount of stress that the steel can withstand and still return to its original shape when unloaded. The first time a trailer is overloaded, the steel will return to something close to the shape it was in when it came off of the manufacturing line, but not exactly to that original shape. Each time it is overloaded, the steel will return to something less than the shape it was in the time before. Eventually, the steel will break.
It can be tempting to look at a trailer's capacity rating and stop there. But, for a true sense of how much a trailer can handle and how it will hold up under the stresses of a specific operation, with its individualized loads, geographies, weights and other variables, contractors need to consider everything that goes into that rating. Purchasing the right trailers for updating a fleet can be complicated and, clearly, the decision is an important one.
Low-quality components wear faster and fail earlier, which contribute to excessive downtime for repairs. That's not including any external factors and costs, such as liability risks with an overloaded trailer failing in a key traffic area or fines due to loads that aren't properly distributed.
