There are five major contributing factors to capacity ratings. Each of these factors can be customized to the operation’s needs. These are the factors to keep in mind:
Load Concentration and Deck Length
There are no industry standards when it comes to determining capacity ratings. To ensure maximum utilization, operators need to pay special attention to load concentration, or the length of the deck that can handle the rated weight. Of course, a 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. While one trailer might need the entire 26 feet to be rated at 50 tons, another can handle that same weight in half the deck length. Since loads are rarely 26 feet long, these ratings give a more realistic indication of the concentrated loads the trailer will be able to handle safely and without structural failure.
Load Distribution and Axle Configuration
How a load is distributed over the deck and the number of required axles is also an important consideration when selecting the right trailer. Axle weight laws and regulations vary from state to state, so fleet managers and operators should work with manufacturers to define the best trailer for the cargo and the best axle configurations to maximize the load in their area of operation.
There are many options for achieving the best possible weight distribution over the axles, depending on the specific state’s regulations and the nature of the load. For example, carriers can vary gooseneck lengths in the front, alter the distances between axles and axle groups, move the load closer to one end or the other, or use a jeep dolly to add extra axles. However, these options must be included in the initial trailer design — simply adding them afterward risks the structural integrity of the trailer and the safety of operators and the public.
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Traveling Speed
Another capacity determinant is speed. While some manufacturers rate their trailers at 55 mph, others rate them at 65 mph. The slower a rig travels, the less added weight or stress is placed on the trailer. The impacts of road dynamics such as potholes, railroad tracks, and so on decrease as speed decreases.
Safety Ratings
A trailer’s safety rating also comes into play when discussing capacity. The safety rating is an indicator of how much stress a trailer can safely handle. It encompasses factors such as the strength of the raw materials used in the trailer’s construction and how the beams and cross members are configured.
The widely accepted average magnification of payload weight on a trailer due to road dynamics is a 1.8 to 1 ratio. However, on any given haul, stress on the trailer can go above that level multiple times. If no cushion is built in to handle those spikes in stress, there is potential for long-term, progressive structural damage. That’s why some manufacturers use a ratio of 2.5 to 1, which is considered an ample cushion for even the most extreme road dynamics a trailer might encounter.
Not only does the safety rating tell a carrier how strong the trailer is, but it’s also a very good indicator of potential life. Typically, the greater the difference is between the static design safety factor and the dynamic 1.8 average multiplier, the longer a trailer’s useful life expectancy.
Manufacturing Materials
Safety factors are strongly related to the quality of the components incorporated into the trailer, such as steel and deck material.
There are several options when choosing steel, but for the highest capacity and smallest impact on the trailer weight, look for a T1 material with a 100,000-psi minimum yield. T1 has maximum strength versus ductility and equates to a lighter, stronger trailer frame.
A trailer’s decking is continually exposed to the elements, making durable decking with a long wear life crucial. Tightly woven and incredibly dense, Apitong decking provides a tougher, longer-lasting wood in comparison to other varieties, such as oak or pine. It’s also less susceptible to chipping and cracking and provides some amount of traction in comparison to a smooth metal surface.
Troy Geisler is the Vice President of Sales and Marketing for Talbert Manufacturing. He has more than 20 years of experience in the trailer industry, including 10 years with Talbert. He earned his bachelor’s degree from Purdue University in West Lafayette, Indiana.
Photos courtesy of Talbert Manufacturing
