How to correctly load a semi-trailer?

Loading a trailer with a heavy load often involves some planning to ensure proper axle weight distribution. Incorrect weight distribution can compromise vehicle stability and impede braking efficiency.

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Lightly loaded axles have less traction compared to fully loaded ones. Mismanagement of load distribution can lead to overload on the suspension, which may result in fines for exceeding legal weight limits.

Understanding how to position your cargo on the trailer blends scientific calculation with practical creativity. It becomes easier when dealing with uniform loads like pallets of similar weights. However, with a mix of various cargo, innovative solutions are often required.

Begin by weighing your truck to establish its empty axle weight. Most highway tractors weigh between 18,000 and 21,000 lb., while tandem van trailers typically weigh around 15,000 lb. Keep in mind that more complex trailer configurations such as tridems and refrigerated trailers will weigh more.

It is crucial for drivers to familiarize themselves with both state and provincial regulations regarding vehicle weight limits and the unladen weights for their trucks. (Illustration: Transportation Warehouse Optimization)

Begin with Your Truck Weight

Position your fifth wheel and trailer axles into a standard configuration, ensuring that the kingpin is slightly ahead of the drive axle's center and the trailer axles align with the 41-foot requirement for legal compliance. Ideally, have full fuel tanks for a realistic weight scenario.

For clarity, let's say an empty five-axle dry van tractor-trailer weighs 35,000 lb. A typical distribution might look like the following:

• Steer axle: 11,000 lb. (4,990 kg)
• Drive axles: 14,000 lb. (6,350 kg)
• Trailer axles: 10,000 lb. (4,353 kg)
• Tare weight: 35,000 lb. (15,875 kg)

For reference, in the American system, the steer axle limit is 12,000 lb., while the drive and trailer axles each have a limit of 34,000 lb. While these numbers may vary in Canada, the same principles apply.

This means your maximum payload could be 1,000 lb. on the steer axle, 20,000 lb. on the drives, and 24,000 lb. on the trailer axle, culminating in a gross vehicle weight of 80,000 lb.

Before proceeding, assess the weight indicated on the bill of lading or cargo manifest; does it account for pallet weight and associated dunnage? Is the shipper trustworthy when reporting cargo weight? Can your truck handle the proposed weight?

If aware of your tare weight beforehand, you can ascertain if loading is feasible. Once loaded, it’s your responsibility to ensure compliance with weight limits or request a reduction in cargo weight from the shipper. Be mindful that even if overall weight remains under legal limits, axle groups can exceed limits, resulting in penalties.

When arranging pallets, aim for a load of around 800 pounds per trailer foot. Utilize averages when dealing with irregular weights, placing heavier pallets in the center and securing lighter ones in the front and rear. (Illustration: Transportation Warehouse Optimization)

A Million Possibilities

A standard 53-foot trailer can accommodate anywhere from 26 to 30 pallets sized 40"x48", depending on orientation. Arranging pallets straight in will allow for 26 pallets, whereas turning half may increase this to 30. A full load tightens placement options, necessitating a careful balance to avoid affecting axle weight negatively.

In contrast, a load comprising 11 pallets, each weighing 4,000 lb., or a mixed load with varied dimensions, complicates matters further.

Don’t forget the significance of cargo securement. Roadside inspectors often check inside trailers, and unrestrained cargo can draw their attention. Proper loading doesn’t just concern axle weights; it’s essential that cargo is secured to prevent movement en route.

A useful starting point is arranging cargo to visualize an equivalent of 800 lb. per foot of trailer space. For instance, two side-by-side 48" pallets could collectively weigh up to 3,200 lb. Managing such variables properly is key.

While isolating pallets can violate the principles of cargo securement, it is frequently necessary to achieve effective weight distribution. (Illustration: Transportation Warehouse Optimization)

Other Considerations

Nevertheless, loading is rarely straightforward. Suppose you are faced with 18 pallets each weighing 2,500 lb., resulting in a total of 45,000 lb. If loaded together from the front to 36 feet forward, this weight distribution may leave the drive axles overloaded while the trailer axles remain underweight.

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By staggering pallet arrangements, for instance, two side-by-side, followed by a single pallet, and continuing that manner towards the rear of the trailer, you could load strategically up to the 48-foot mark just above the trailer axles. This way, you achieve roughly 7,500 lb over eight feet, aligning closer to your goal of 800 lb per foot.

Consider placing two single pallets upfront, balancing the drive axles which tend to carry more weight than the trailer axles when unloaded. Think of a loading pattern like 2-1-1-2-1-1-2-1-2 towards the rear, ensuring a stable distribution.

When pallets are expertly secured, such as being tightly shrink-wrapped, their stability increases in transit, minimizing the risk of shifting.

Average That Weight

For diverse pallet weights, use a calculator to determine suitable side-by-side arrangements that total approximately 800 lb. per foot. This may warrant a loading pattern that extends to eight- or twelve-foot intervals rather than sticking strictly to four-foot (48-inch) sections.

Here, the fusion of art and science in loading becomes apparent. Aim for balanced weight distribution longitudinally while allowing for slight variations to place heavier loads towards the center and lighter at the ends. This method helps attain a more uniform weight spread across the trailer length.

You might look at configurations across eight-to-twelve-foot segments. For instance, positioning a 3,000 lb. pallet alongside a 2,000 lb. pallet, followed by 1,500 and 2,500 lb. pallets, can yield a balanced approach, hitting around 11,000 lb over 12 feet, which remains within logical parameters.

Be cautious of gaps that result from using single pallets; avoid them as much as possible. It's worth noting that some shippers provide materials like cardboard dunnage or inflatable air bags for void filling. Key cargo restraint systems include straps, decking bars, and load locks—but reliance solely on load locks as restraints is ill-advised. They often fail to meet compliance in the event of inspections, especially if starting a row.

How cargo is positioned affects axle weights significantly. Evaluating cargo placement combines both scientific analysis and creative loading strategies. (Photo: Jim Park)

It's Your Responsibility

In concluding remarks, recognize that many shippers have established methods for loading predictable cargo. However, mixed loads or complex arrangements for multiple drop-offs require more detailed attention.

As the operator of the truck, you bear the ultimate responsibility for how loading is executed. If a shipper's loading procedure raises concerns, communicating directly with a supervisor is vital. It’s wise to err on the side of caution than to risk penalties from overweight tickets.

Ensure particular care with any load approaching within 10,000 lb. of the gross limit. Achieving a proper distribution of 35,000 lb. within 30 feet requires balanced placement to avoid front-heavy conditions.

Maintain records of empty truck weights, loading configurations, and weight distributions post-loading. As you familiarize yourself with axle weight distribution, your loading strategies will improve.

Furthermore, Transportation Warehouse Optimization has developed worksheets illustrating effective trailer loading methods. These resources offer valuable insights for drivers as well.

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