A 4-axle semi-trailer in the U.S. typically supports up to 80,000 pounds, with 20,000 pounds per single axle and 34,000 pounds for tandem axles. Proper weight distribution, like 12,000 pounds on the steer axle, ensures compliance and maximizes safety during transport.

United States (Federal Standards)

The legal weight for a 4-axle semi-trailer is provided in the United States by specific axle weight limits and overall GVW regulations. According to the Federal Bridge Formula, the single axle can carry 20,000 pounds maximum, and the tandem axles, 34,000 pounds maximum. This configuration allows the typical 4-axle semi-trailer a maximum GVW of 80,000 pounds for the truck's weight plus trailer and cargo. This keeps traffic safe on the highways while allowing a substantial amount of payload. For example, a loaded semi-trailer could be carrying 40,000 pounds of consumer goods and itself weigh 36,000 pounds, yet still be within federal limits and provide a dependable transport solution for logistics companies.

Often to stay within legal limits, operators use a 12,000 pound-rated steer axle and distribute the rest of the weight across the other axles. That same truck loaded with 48,000 pounds of excavated construction materials could then safely carry 12,000 pounds on the steer axle and 17,000 on the first two trailer axles, leaving 14,000 pounds on the last axle. Good distribution avoids overloading fines that can run into thousands of dollars per violation, depending on the state and weight excess.

A 4-axle semi-trailer is very effective for special freight requiring balance load distribution without exceeding federal limits. One single trip with 30,000 pounds of farm products, such as wheat or corn, generates a good deal of value for farmers and distributors. In comparison, a heavier haul of 75,000 pounds of gravel for construction would require additional permits to stay in compliance, while the need for load management is important. Such trailers are often employed because they are able to work with a wide range of freight options while still being very flexible on many different types of roads.

European Union

The European Union has set the weight that a 4-axle semi-trailer can carry to a weight that will maximize road safety, infrastructure durability, and efficiency in freight. The average weight allowed for a 4-axle semi-trailer is about 36,000 kgs (79,366 pounds). The weight here is for both tractor and trailer with cargo combined. A typical distribution could be 10,000 kg (22,046 pounds) for the steering axle and 26,000 kg (57,320 pounds) for the remaining three axles to stay within EU road standards. A typical example would be a 4-axle semi-trailer carrying 25,000 kg (55,116 pounds) of construction equipment and having an unladen weight of 10,000 kg (22,046 pounds) falling well within those limits.

The European Union has particular axle weight limits to control road stress and increase safety. For example, a single axle can only carry 10,000 kilograms, or 22,046 pounds, whereas a tandem axle can carry 18,000 kilograms, or 39,683 pounds, under most road classifications. A truckload of 35,000 kilograms, or 77,162 pounds, of industrial items would normally divide the weight for conformance with these limits, perhaps with 9,000 kilograms, or 19,841 pounds, on the steering axle and 26,000 kilograms, or 57,320 pounds, on the trailer axles. The reason for these limits is to minimize the occurrence of road damage and ensure that goods are transported efficiently.

The operating cost of a 4-axle semi-trailer truck in the EU depends on its weight, fuel consumption, and maintenance needs. A fully loaded 4-axle truck usually covers 1,000 kilometers (621 miles) using 400 liters (105 gallons) of diesel with an average price of €1.90 per liter, hence incurs a fuel cost of €760 per trip. Besides that, the overloaded may be fined from €500 to €5,000 according to the case seriousness. Complying with weight controls cuts down on these risks while optimizing all significant operational costs.