Truck

I

Introduction

Truck, motor vehicle designed primarily for hauling cargo or for special work or service purposes. Trucks are usually larger and heavier than automobiles and differ in basic construction. Most modern automobiles have a unibody construction, in which the body itself provides structural support for the vehicle. Trucks, by comparison, are built around a strong metal frame, called a chassis, that supports the rest of the truck. Trucks usually have larger, more powerful engines and stronger suspensions than automobiles have. Large trucks have additional axles and wheels for carrying heavy loads.

Trucks come in many different varieties and are classified by weight, type, and the job they perform. Light trucks have a vehicle weight of up to 6,300 kg (14,000 lb) and are used for light hauling or towing, as well as for everyday transportation. Medium trucks have a weight of up to 15,000 kg (33,000 lb) and are typically used as dump trucks, garbage trucks, local freight-delivery trucks, and utility vehicles. Light and medium trucks are usually powered by gasoline internal-combustion engines, although some may be powered by diesel engines. Heavy trucks are over 15,000 kg (33,000 lb) in weight and are used primarily to pull trailers. Such trucks are often called semis (short for semitrailer), or tractor-trailer trucks, and use large diesel engines for power. Heavy trucks also include large vehicles designed for off-road work, such as large construction and mining trucks.

Trucks are also classified by their construction. Straight trucks have the body, or cab, and cargo compartment mounted on the same frame. All light trucks and most medium trucks are straight trucks. In a tractor-trailer truck, the engine and cab are part of the tractor unit. The trailer is a detachable unit, is separate from the tractor, and has its own suspension and wheels. It is joined to the tractor by a hinged platelike mounting device called a fifth wheel.

II

Light Trucks

Light trucks include pickup trucks, minivans and full-size vans, and sport utility vehicles (SUVs). The engines, transmissions, and brakes of light trucks are usually similar to those used in passenger cars. Some light trucks offer four-wheel drive for off-road driving or driving on mud or snow. Light trucks are often used as passenger cars are for everyday driving, particularly in rural areas, but they also provide the ability to carry extra cargo when needed. They are used primarily for light hauling and construction work.

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Most pickup trucks have a cab with two doors and a single bench seat that holds up to three passengers. Some have extended cabs with a rear seat or additional doors. The cargo area behind the cab is called the bed. It has raised sides and a fold-down tailgate at the back for loading and unloading cargo.

Vans are mechanically similar to pickup trucks, except that the cargo area is enclosed and is part of the body. Vans typically have side doors and a rear door in addition to the front doors. A cargo van is equipped with only a front seat, and the unfinished rear area is reserved for hauling items. Cargo vans are often used to deliver small parcels and goods in urban areas. A passenger van has multiple seats for carrying extra passengers, as well as side windows. Some have lengthened bodies to carry up to 15 or more passengers and are used like small buses. A conversion van is a cargo van that has been specially modified to carry passengers in luxury. Conversion vans typically have plush interiors, numerous accessories, and individual seats. Minivans are smaller vans intended primarily for hauling six to eight passengers. Minivans have mostly replaced station wagons as a family vehicle. Some minivans have rear-wheel drive, but most have front-wheel drive. They also have the same engines, transmissions, and suspension components as front-wheel-drive passenger cars. In addition to the two front doors, most minivans have one or two sliding side doors and a rear liftgate that opens vertically.

Many light trucks are adapted for special uses. Tow trucks have a derrick and winch for towing vehicles, or a tilting bed for carrying disabled vehicles. Many ambulances are also built on light-truck frames. Large police trucks, nicknamed paddy wagons, have an enclosed confinement area in the back for transporting groups of people who have been arrested. Some police departments in large cities also have specially armored trucks for use by riot teams or bomb disposal units.

III

Medium Trucks

Medium-duty trucks have larger engines and frames than do light trucks and often have dual rear wheels or a second rear axle for carrying additional weight. Medium trucks are used primarily for local delivery work, for construction, and by municipal and utility fleets. Dump trucks have a hydraulically powered bed that tilts up and down for hauling and dumping rock, gravel, dirt, and debris. Garbage trucks have a large enclosed compartment and a hydraulic compressor for compacting and hauling refuse. Utility trucks with a boom and basket, nicknamed cherry pickers, are used by utility companies for lifting people up to work on utility lines or trees. Fire engines often have a large internal water tank and pump for fighting fires. Some carry large ladders for reaching the upper floors on multistory buildings. See Fire Fighting.

IV

Heavy Trucks

Heavy trucks have the largest frames and are usually powered by large diesel engines. They have multispeed transmissions, with as many as 18 gears, for pulling heavy loads. Most semis or tractor-trailer trucks have two rear drive axles, called dual tandems, each of which has dual tires on each side. Trucks with this arrangement are nicknamed 18-wheelers because of the total number of wheels under the truck and trailer.

When a heavy truck is assembled, the type of engine, transmission, brakes, axle arrangement, and other equipment used are usually specified by the individual or company that is ordering the truck. Almost all heavy trucks have power steering, cruise control, and air brakes. Air brakes use compressed air, rather than brake fluid, to activate and release the brakes. An air reservoir in the truck supplies air to the brakes through air hoses. The constant supply of air keeps the brakes released. Pressing on the brake pedal decreases the air pressure and applies the brake. If the brake system malfunctions or if the air hoses become punctured, the brakes apply themselves automatically as a safety precaution.

Most heavy trucks are designed for hauling goods over long distances, known as over-the-road hauling, although some are also used for local deliveries. The truck cab may be positioned behind the engine and hood or located directly over the engine. The latter is called a cab-over design, and it reduces the overall length of the truck-trailer combination. Cab-over trucks are hinged to tilt forward when engine access is necessary for maintenance or repairs. Most long-haul heavy trucks have a sleeper compartment, behind the cab, that contains a bed for the driver. The sleeper compartment is the truck driver’s home away from home and may be equipped with a television, a microwave oven, and a refrigerator. Most heavy trucks are also equipped with citizens band radio for communication. Some truck fleets use satellite tracking equipment to monitor their trucks, so the fleet operator or dispatcher can know a truck’s location at any time.

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