TRUCK INDUSTRY TERMS & TRUCKING GLOSSARY

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- D -

Dead-Heading
Operating a truck without cargo.

Demountable Rim
Multi-piece steel wheel rim assembly which is bolted to a spoke hub. Demountable rims are still in use, though they have been replaced in many applications by the simpler disc wheel. (see Cast Spoke Wheel)

Disc Wheel
Single-piece rim/wheel assembly of stamped and welded steel or forged aluminum, anchored by 8 or 10 nuts to a hub. A "Budd wheel" is a ten-hole, stud-piloted disc wheel; a design originated by the Budd Corporation.

Displacement (Piston Displacement)
Sum of the volumes swept by an engine's pistons as they travel up and down in their cylinders. Based upon bore (diameter of cylinder) and stroke (distance traveled by piston). Expressed in liters or cubic inches.

Doubles (Twins, Twin Trailers)
Combination of a tractor and two semitrailers connected in tandem by a converter dolly.

Driveline
All the components which together transmit power from the transmission to the drive axle(s). These consist of at least one driveshaft (propeller shaft) with a universal joint at each end.

Drivetrain (Powertrain)
All the components, excluding engine, which transmit the engine's power to the rear wheels: clutch, transmission, driveline and drive axle(s).

DRL (Daytime Running Lights)
System that automatically turns on a vehicle's low beam headlights when the parking brake is released and the ignition is on.

- E -

EDI (Electronic Data Interchange)
The business-to-business interconnection of computers for the rapid exchange of a wide variety of documents, from bills of lading to build tickets at auto plants.

Exempt Carrier
Company which transports commodities exempted from Interstate Commerce Commission (ICC) economic regulation.

EV (Electric Vehicle)
Vehicle powered by electric motor(s) rather than by an internal combustion engine. Most common source of electricity is chemical storage batteries.

- F -

Fifth Wheel
Coupling device attached to a tractor or dolly which supports the front of a semitrailer and locks it to the tractor or dolly. The fifth wheel's center is designed to accept a trailer's kingpin, around which the trailer and tractor or dolly pivot in turns.

Fixed Tandem
Assembly of two axles and suspension that is attached to the chassis in one place, and cannot be moved fore and aft.

For-Hire Carrier
Company in the business of transporting freight belonging to others

- G -

GAWR (Gross Axle Weight Rating)
Maximum weight an axle is rated to carry by the manufacturer. Includes both the weight of the axle and the portion of a vehicle's weight carried by the axle.

GCW (Gross Combination Weight)
Total weight of a loaded combination vehicle, such as a tractor-semitrailer or truck and full trailer(s).

Geared Speed
Calculated vehicle speed at the engine's governed rpm in each transmission gear, or (commonly) in top gear.

Gear Ratio
Number, usually expressed as a decimal fraction, representing how many turns of the input shaft cause exactly one revolution of the output shaft. Applies to transmissions, power takeoffs, power dividers and rear axles. Example: If 2.5 revolutions of an input shaft cause one revolution of the output shaft, the gear ratio is 2.5:1.

Grade
Steepness of a grade, expressed as a percentage. Example: A vehicle climbing a 5% grade rises 5 feet for every 100 feet of forward travel.

Gradeability
Vehicle's ability to climb a grade at a given speed. Example: A truck with a gradeability of 5% at 60 mph can maintain 60 mph on a grade with a rise of 5%.

GVW (Gross Vehicle Weight)
Total weight of a vehicle and everything aboard, including its load.

GVWR (Gross Vehicle Weight Rating)
Total weight a vehicle is rated to carry by the manufacturer, including its own weight and the weight of its load.

- H -

Hazmat
Hazardous materials, as classified by the U.S. Environmental Protection Agency (EPA). Transport of hazardous materials is strictly regulated by the U.S. Department of Transportation.

Headache Rack
Heavy protective barrier mounted behind the tractor's cab. Designed to prevent "headaches" caused by load shifting forward from the trailer and crushing the cab.

HCFC
Hydrochlorofluorocarbon.

Horsepower (hp)
Measure of power (the amount of work that can be done over a given amount of time). One horsepower is defined as 33,000 foot-pounds of work in one minute. Example: Lifting 33,000 pounds one foot in one minute, or lifting 3300 pounds ten feet in one minute.

Horsepower, Gross Laboratory
Tested horsepower of a "bare" engine without fan, water pump, alternator, exhaust system or any other accessories.

Horsepower, SAE Net
Horsepower capability of an engine with full accessories and exhaust system. Test procedures per standards of Society of Automotive Engineers (SAE).

Hours-Of-Service
U.S. Department of Transportation safety regulations which govern the hours of service of commercial vehicle drivers engaged in interstate trucking operations.

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