Heavy-Duty Truck Information
Thursday, October 2nd, 2008Trucks are divided into light-duty truck, medium-duty truck, and heavy-duty truck classifications depending on their weight. Heavy-duty trucks have a gross vehicle weight of 33,000 lb (15,000 kg) or more (i.e. the weight of the vehicle plus the weight of the payload is 33,000 pounds or more). When a heavy-duty truck is pulling a trailer, it may have a gross combination weight of 80,000 lb (36,360 kg) or more.
Technically, a vehicle that carries the load by itself, without a trailer, is known as a truck, or a straight truck. Examples include certain dump truck, concrete mixers, and garbage trucks. A vehicle that pulls the load in a trailer is known as a tractor. The tractor is coupled to the trailer through a pivot point, known as the fifth wheel, which is mounted on top of the tractor frame. Most of the big rigs on highways are tractors pulling trailers.
The first gasoline-engine trucks were developed in the United States in the 1890s. During World War I, trucks played an important role moving supplies at home and overseas. With the development of a system of paved roads in the United States during the 1920s, the number of truck manufacturers grew. By 1925, there were more than 300 brands of trucks on the road. Some manufacturers came and went quickly. The Great Depression of the 1930s finished many more. By the 1990s, there were only nine heavy-duty truck manufacturers left in the United States. Together they build about 150,000-200,000 trucks a year.
Trucks use steel for strength and durability, aluminum for light weight and corrosion resistance, polished stainless steel for bright finishes, and molded plastics for complex shapes.
Frame rails and crossmembers are usually formed from high-tensile steel. Suspension components, axles, and engine mounts are also made from steel. Some are cast and some are fabricated and welded.
The cab structure and outer skin may be made from steel or aluminum. If steel is used, the metal is coated with one or more layers of corrosion barriers such as zinc. On some cabs the roof may be made of fiber-glass to form the complex curves required at the corners.
The hood and front fenders are usually molded in plastic or fiberglass because of the complex aerodynamic shapes. The front bumper may be stamped and drawn from steel or aluminum, or it may be molded in plastic and backed with a steel substructure.
Truck manufacturers usually design a new model about every five to seven years. The new design incorporates advances in technology and materials, as well as changes desired by the customers. The design team will use a clay model to determine the overall styling, then build a prototype cab and hood for review and durability testing. As the design progresses, they will build an entire prototype vehicle for road testing. Just before the new truck goes into production, they will build one or more pilot models using actual production parts to spot any last-minute assembly problems.
In addition to the basic model, the engineers must also design all the options required by customers for different truck applications. Some manufacturers have as many as 12,000 options for their line of heavy-duty truck models.
