What are the components of a combination vehicle?
Truck drivers may drive many types of Commercial Vehicles. A combination vehicle is formed when a truck tractor or straight truck has a trailer added to it.
What are the basic terms that describe a combination vehicle?
Truck Tractor (Power Unit)
Truck tractor is a power unit (with an engine) that is self-propelled and pulls one or more trailers.
Steering axle is the front axle that controls vehicle direction
Drive axle is the axle (or axles) in the back of the tractor that are powered by the engine and transmission to pull the load.
Tandem axle is when there are two axles on the tractor or the trailer (or both). Some tractors are single axle, and some are tandem axle.
Dual Tires are when there is a pair of wheels and tires that are located on one side of one axle. A tandem axle tractor will have 4 sets of dual tires.
Fifth wheel is a coupling device located on the tractor’s rear frame mounted over the tractor axles. The fifth wheel is how the tractor is connected to a trailer.
Converter dolly is a device that has an axle with a set of wheels, and a fifth wheel on top that is typically used to connect one semi-trailer to another trailer. The dolly “converts” a semi-trailer to a full trailer.
What are the different types of trucks or tractors?
Conventional tractor: typical U.S. tractor, with the engine and front axle placed in front of the driver, usually with a longer hood
Straight truck: Has one continuous frame and does not “articulate” (or bend) as a combination vehicle would.
Cabover tractor: typically seen in Europe, these tractors are configured so the driver sits over the engine and front axle (“cabover”)
Single Drive Axle Tractor
Tandem Axle Tractor
Day Cab vs. Sleeper Tractor
A day cab has no sleeping area, whereas a sleeper has room for the driver to rest.
Dual Wheels vs. Super Singles
Dual wheels vs. super singles: uses large and wider tires rather than dual tires
What are the different types of trailers?
A trailer is a vehicle designed to haul cargo.
A “semi-trailer” connects to a tractor by the fifth wheel that is mounted over the tractor axle. A semi-trailer only has axles in the rear, not the front.
A “full trailer” has axles in the front and rear. A full trailer is made by attaching a “converter dolly” to a semi-trailer
There are many different types of trailers with various uses:
Van: hauls general freight in a dry environment
Liquid Tanker: hauls liquids such as milk or fuel
Flatbed: hauls large and bulky objects like steel or lumber
Lowboy or Drop-Deck: has various configurations usually to haul heavy equipment for construction or farms
Dry Bulk: used to carry bulk material like powder or pellets
Reefer: Refrigerated van that hauls food that is kept cold
Container Chassis: hauls containers that are used in “intermodal” transport (more than one mode of transport – for example ship, rail and truck)
What are the different arrangements of wheels and axles for combination vehicles?
Combination rigs have many different configurations.
There are several axle arrangements on a standard tractor and semi-trailer combination:
There are numerous trailer combinations on U.S. highways. Some combinations are only allowed on certain roads