Commonly Used Terms and Definitions
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- Above-cab Carrier
- A platform above the cab that can be in a fixed or hydraulically adjustable position for transporting vehicles.
- Accessory Load Electrification
- The conversion of common vehicle accessory loads (power steering, power brakes, air conditioning, air compressor, etc.) from being engine-driven (belts or gearing) to being driven by electric motors. Electrically driven systems can be optimized to operate at a fixed speed, thereby increasing efficiency and making them compatible with hybrid vehicle propulsion systems.
- AF (Axle-to-Frame)
- The distance from center of rear axle(s) to end of frame. See Chassis Dimensions.
- Air Dam
- Flexible air deflecting panel usually located below the radiator support.
- Air Resistance
- A measure of the “drag” on a vehicle moving through air. Air resistance increases as a square of the speed, thus power requirements increase much faster than vehicle speed.
- Alternative Drive Systems
- Any vehicle drive (propulsion) system other than a conventional internal combustion/mechanical transmission system. The most common systems are straight electric, hybrid electric and hybrid hydraulic drives.
- Alternative Fuel
- Any non-conventional fuel used to power a vehicle. In North America, conventional vehicle fuels are normally defined as gasoline and petroleum-based diesel. Alternative fuels currently in use or under development include:
- E-85 — A blend of 85% ethanol and 15% gasoline that is used to fuel E85-capable flexible fuel vehicles (FFVs), which are available in a variety of models from U.S. and foreign automakers.
- Biodiesel — A liquid fuel composed of fatty acid alkyl esters, fatty acid methyl esters or long-chain mono alkyl esters. It is produced from renewable sources such as new and used vegetable oils and animal fats, and is a cleaner-burning replacement for petroleum-based diesel fuel. It is normally blended with conventional petroleum-based diesel fuel for use.
- B-10 — A blend of 10% biodiesel and 90% petroleum-based diesel fuel.
- B-20 — A blend of 20% biodiesel and 80% petroleum diesel. B-20 is the most common biodiesel blend in the U.S. It provides substantial benefits but avoids many of the cold-weather performance and material compatibility concerns associated with B-100 (pure biodiesel).
- Compressed Natural Gas (CNG) — Natural gas is a mixture of hydrocarbons; predominantly methane (CH4). When used as transportation fuel, it is typically stored onboard a vehicle in tanks at high pressure (up to 3,600 PSI).
- Electricity — Electricity used to power pure electric vehicles (as opposed to electric hybrids) is generally provided by the electricity grid and stored in a vehicle’s battery. Fuel cells are being considered as a way to use electricity generated onboard the vehicle to power electric motors. Unlike batteries, fuel cells convert chemical energy from hydrogen to electricity (see Electric Drive Vehicle).
- Hydrogen — The simplest and most abundant element in the universe. The interest in hydrogen as an alternative transportation fuel stems from its clean-burning qualities, its potential for domestic production and the fuel cell’s potential for high efficiency (two to three times more efficient than gasoline vehicles).
- Liquefied Natural Gas (LNG) — Natural gas can be liquefied to store more energy onboard a vehicle in a smaller volume. To produce LNG, natural gas is purified and condensed into liquid by cooling to –260°F (–162°C). Since it must be kept at such cold temperatures, LNG is stored in double-wall, vacuum-insulated pressure vessels. LNG fuel systems are typically only used with heavy-duty vehicles.
- Propane — A three-carbon alkane gas (C3H8), also known as liquefied petroleum gas (autogas in Europe). Propane turns into a colorless, odorless liquid when stored under pressure inside a tank. As pressure is released, the liquid propane vaporizes and turns into gas that is used for combustion or that can be injected, under pressure, as a liquid fuel. An odorant, ethyl mercaptan, is added for leak detection.
- Ambient Temperature
- Surrounding air temperature.
- Anchor Bar
- Part of the tow sling or tow hitch that is placed under or against a vehicle to be towed. It must be fastened to the vehicle with two tow chains.
- Approach Angle
- (1) Ramp clearance angle for the front of a vehicle, measured from the forward edge of the front tire contact patch to the lowest part of the vehicle forward of the tire; (2) An angle made between the plane of the platform and the ground plane on a carrier body.
- Auxiliary Engine
- A small internal combustion engine carried on a vehicle to for purposes other than direct power. Typical uses include operation of refrigerator units, electric generators and welders, and vehicle-mounted equipment, such as cranes and aerial devices.
- Auxiliary Equipment
- Fuel tanks installed in addition to the standard equipment tank.
- Auxiliary Fuel Tanks
- A type of drive axle in which the axle "floats" in the axle housing with all the truck weight and stress of the wheels on the housing, not the axle shaft.
- Auxiliary Towing Lights
- Stop, tail and turn-signal lights attached to the trailing end of the towed vehicle operated as part of the towing vehicle lighting system.
- Auxiliary Transmission
- A transmission with a limited number of speeds (usually two, three or four) that is mounted immediately in back of the main transmission. The auxiliary has its own control in the cab, and by using both transmissions the driver can get several times the number of forward speeds possible with just the main transmission. A five-speed main transmission with a three-speed auxiliary would give the driver 15 forward speeds.
- A means of support for the wheels at each end. This is contrasted to a Live Axle, which is connected to the wheels and rotates with the wheels.
- The axle that is connected to the truck engine and propels the truck.
- Axle-Full Floating
- A type of drive axle in which the axle “floats” in the axle housing with all the truck weight and stress of the wheels on the housing, not the axle shaft.
- A means of support for the wheels at each end that connects the wheels with members that rotates with the wheels.
- A type of drive axle in which the weight of the truck, with consequent load and wheel stress, is supported by the axle shaft.
- Axle-Tandem Drive
- Both axles of the tandem are driven by the vehicle engine.
- Axle Rating
- See Gross Axle Weight Rating.
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- The distance from the foremost point on the front bumper to the center line of the front axle. See Chassis Dimensions.
- A plate or shield used for deflecting, checking or regulating the flow of liquids or gases.
- The cylindrical component of the hydraulic cylinder.
- An electro-chemical device for storing electrical energy.
- The distance from the foremost point on the front bumper to the back of the cab.See Chassis Dimensions.
- Bending Moment
- The force times the distance from the support to the point the force is applied causing bending.
- Bevel Gear
- Gear that will transmit power at an angle.
- Abbreviation for Brake Horsepower. See Horsepower.
- BL (Body Length)
- The distance from the foremost point of the body to the rearmost point of the body. See Chassis Dimensions.
- A tank vehicle accessory (that may be either tractor-mounted or trailer-mounted) used in the transfer by air of dry bulk products at pressures normally below 5 psi.
- The structure or that portion of the vehicle that carries the load or cargo.
- Body Extension Over Cab
- A body overhang commonly found in furniture vans. Also referred to as Attic, Boot, Bullnose, Chair Deck, Peak or Poop Deck.
- Body Hinge
- The attachment mechanism connecting a tilting body to the stationary frame about which the body rotates into the tilt position.
- Body Subframe
- Another term for Body Understructure or Mounting Subframe.
- Body Understructure
- Crossmembers and longitudinal members under the body floor.
- Body Weight
- Unmounted weight of a body with applicable options.
- The transverse members commonly used to define the horizontal support for the diagonal braces of a vertical mast.
- A member extending from a mast, base, or frame, to hold, extend or lift a load.
- Bore and Stroke
- Bore is the diameter of the engine cylinder. Stroke is the maximum distance the piston moves.
- Brakes: Emergency
- An independently actuated secondary brake system used for parking or in an emergency when the service brake is inoperative.
- Brakes: Engine
- The engine's compression pressure used for retarding the truck.
- Brakes: Service
- Mechanism for retarding and stopping the truck.
- Bridge Formula
- A formula used by certain states to compute the maximum allowable weight for vehicles. Total weight, number of axles and location of axles are factors in this formula.
- Bumper: Dock
- A bumper attached to the rearmost portion of the body (often called Platform Floor Extension).
- Bumper: DOT
- A bumper designed to provide rear end protection that meets requirements of FMCS 393.86. Previously called ICC Bumper, ICC Drop Bumper or Step Bumper.
- Bumper: Step
- A light truck bumper with a flat top surface to provide a step for entry into a truck body.
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- CA (Cab-to-Axle)
- The distance from the back of the truck cab to the center of the rear axle. Clear or effective CA is the distance from the rear surface of any obstruction behind the cab to the center of the rear axle. On a tandem-axle truck this dimension is from the back of the cab to a point midway between the two rear axles. See Chassis Dimensions.
- The driver passenger carrying compartment of a chassis cab.
- Cab Control Levers
- Handles to control action of power take off and hydraulic valve, usually located in truck cab convenient to driver's hand.
- Cab Forward
- See Forward Control.
- Cab Over Engine (COE)
- Cab design where driver is actually as far forward as possible. Engine is directly under cab.
- Cab Protector
- Metal shield over the cab as protection from cargo such as coal, stone, etc. being loaded into a dump body.
- Cab to Tandem (CT)
- The distance from the back of the cab to a point midway between the tandem axles. Clear or effective CT is the distance from the rear surface of any obstruction behind the cab to the center of the rear axles.
- Steel wire rope used for pulling or supporting.
- The angle a front wheel makes with a vertical line. Outward lean on the top of a wheel is "positive camber".
- Cargo Weight Rating
- The value specified by the manufacturer as the cargo-carrying capacity, in pounds, of a vehicle, exclusive of the weight of the occupants (computed at 150 lbs. times the number of designated seating positions).
- A platform body with a winch for loading.
- The angle a front wheel spindle pivot makes with a vertical line. Tilting the top of the pivot to the rear of the vehicle is "positive caster."
- CB (Cab-to-Body)
- The distance between truck cab and body. See also Chassis Dimensions
- CE (Cab-to-End of Frame)
- The dimension from the back of the cab to the rear of the standard frame. Used primarily to determine size of body which may be used. See Also Chassis Dimensions
- CG (Center of Gravity)
- The point at which the weight of the chassis, body equipment, and payload, if collectively or individually supported, would balance vertically, horizontally, and laterally. (This engineering concept finds the center of the mass of an object.) The three measurements necessary to determine the CG of an object defined as follows: Horizontal (HCG) - Measured fore and aft from a reference plane. Lateral (LCG) - Measured from center line of the vehicle to the side. Vertical (VCG) - Measured up or down from a reference plane.
- Certification Label
- A label, required by Public Law 89-563, that states (certifies) that a motor vehicle or item of motor vehicle equipment complies to all applicable Federal Motor Vehicle Safety Standards in effect on the date of manufacture.
- Rating of diesel fuel similar to octane for gasoline.
- Chassis Cab
- An incomplete vehicle with a completed occupant compartment that requires only the addition of cargo-carrying, work-performing or load-bearing components to perform its intended functions.
- Chassis Dimensions
- Designations commonly used to describe a truck and its components.
- Classification of Trucks by Ground Contact
- Trucks are classified by the number of wheels and the number of driving wheels. If a truck is designated as a 4x2, it has four wheels and two driving wheels. A 4x4 truck has four wheels and four driving wheels. A 6x4 truck has six wheels and four driving wheels. (Wheels are considered a unit whether they have single or dual tires.)
- Clearance Lights
- Lighting to indicate the overall width of the vehicle.
- Common Carrier
- A trucking firm that hauls for hire.
- Completed Vehicle
- A vehicle that requires no further manufacturing operations to perform its intended function, other than the addition of readily attachable components such as mirrors or tires and rim assemblies, or minor finishing operations such as painting.
- Compression Pressure
- The force in pounds per square inch exerted by the compressed charge in the combustion chamber space when the piston is at the top of the compression stroke.
- Compression Ratio
- The cylinder and head volume (piston displacement plus combustion chamber volume) when the piston is at the bottom of the stroke divided by the combustion chamber volume when the piston is at the top of the stroke.
- Contract Carrier
- A trucking firm that has a hauling contract with a certain company or companies.
- Control Lever
- A device for imparting motion into control linkage.
- The front part of an automotive cab or body directly below the base of the windshield between fire wall and dashboard (instrument panel). Used to indicate the complete vehicle (less body) when produced by a factory to include the cowl but not the remainder of the cab or body.
- General term applied to transverse members in the understructure or on a truck frame.
- The inside dimensions of a truck body or trailer expressed in cubic feet. So called "high cube"; equipment is designed to offer the maximum interior load space for its exterior length and width.
- Curb Weight
- The weight of a motor vehicle with all permanently mounted equipment and maximum capacity of engine fuel, oil and coolant. Same as Tare Weight.
- The right or passenger side of the vehicle when viewed from the rear, opposite side from Roadside.
- Curb Weight
- The weight of a motor vehicle with standard equipment; maximum capacity of engine fuel, oil and coolant; and if so equipped, air conditioning and additional weight optional engine.
- A hydraulic cylinder assembly complete.
- Cylinder Base
- End of hydraulic cylinder opposite to header or rod end.
- Cylinder Head
- End of a hydraulic cylinder through which the piston rod extends. Also called Header.
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- Department of Energy (DOE)
- A governmental department charged with advancing the national, economic and energy security of the U.S.; promoting scientific and technological innovation; and ensuring the environmental cleanup of the national nuclear weapons complex. Visit www.energy.gov to learn more. • 21st Century Truck — A DOE Vehicle Technologies Program partnership aimed at developing technologies for the nation’s trucks and buses that could safely and cost-effectively move larger volumes of freight and greater numbers of passengers while emitting little or no pollution and dramatically reducing dependence on foreign oil. Click here to learn more. • National Renewable Energy Laboratory (NREL) — A DOE facility dedicated to the research, development, commercialization and deployment of renewable energy and energy efficiency technologies. Visit www.nrel.gov to learn more.
- Deflection Rate
- Used in rating springs to determine the number of pounds necessary to deflect a spring one inch. For torsion bars, it is a one-inch deflection of the control arm.
- The gear assembly on the drive axle that permits one wheel to turn slower or faster than the other when going around corners.
- Differential-No Slip or Limited Slip
- This type of differential will not allow one wheel to spin while the other is motionless, such as when a truck is stuck on ice or in mud. Torque is transmitted to both drive wheels for better traction. This type of differential is available on almost all cars and trucks today as an option and is standard equipment on some.
- Drive Cycle
- A series of data points (usually presented as a simple line graph) that plot vehicle speed versus time. In some cases, engine RPM is also incorporated to account for conditions such as stationary power take-off operation, off-road operation and operation of power equipment at low road speeds.
- The displacement of an engine is the volume through which the head of the piston moves multiplied by the number of pistons in the engine.
- Diverter Valve
- Auxiliary valve to provide hydraulic power from the hydraulic pump by switching the oil flow from its usual passageways into additional pieces of equipment such as snowplows or other lifting cylinders. Also called Diversion or Selector Valve.
- Dolly (Towing)
- A four-wheel carriage often used in towing to support the trailing end of a vehicle.
- Abbreviation for Department of Transportation, the agency composed of several federal agencies dealing with regulations concerning the manufacture and operation of motor vehicles and motor vehicle equipment.
- Double-bottom Trailer
- A combination consisting of a tractor pulling a semi-trailer with a full trailer in back. Also called Tandem Trailer.
- The total system drive shaft consisting of universal joints, slip yokes and flanges between the transmission and axle(s).
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- Electric Drive Vehicle
- In an electric drive vehicle, torque is supplied to the wheels by an electric motor that is powered solely by a battery; an internal combustion engine using hydrogen, gasoline or diesel; or by a fuel cell.
- Elevating Gate
- A form of endgate used in conjunction with a hydraulic or mechanical hoisting mechanism to allow the gate to descend to ground level. Power elevation allows a gate to be used to raise freight to truck floor level for loading. Also referred to as a Lift Gate, Load Gate, Power Gate or Tailgate Lift.
- Energy Storage Media (Electric)
- Electrochemical devices utilized to store and release electric energy used for operating electric drive vehicles. Types of electric energy storage media include: • Battery — A combination of one or more electrochemical cells used to convert stored chemical energy into electrical energy. Batteries are normally described by their mode of operation (primary cell, which is non-rechargeable, or secondary cell, which is rechargeable); their construction (wet or dry cell); and their construction materials. • Lead Acid — A form of rechargeable battery (secondary wet cell) that uses lead and lead dioxide for the electrodes (charged state) and a dilute solution of sulfuric acid as an electrolyte. Lead acid batteries have a low energy-to-weight ratio but are low-cost and have the ability to supply high surge currents without being damaged. • Lithium Ion (Li-ion Battery) — A type of rechargeable dry cell battery (secondary cell) in which the cathode (positive electrode) contains lithium. The anode (negative electrode) is generally made of a type of porous carbon. The non-aqueous electrolytes used in lithium ion batteries are typically based on patented formulations containing manganese or cobalt salts. Lithium ion batteries have a high energy density; are lighter than other energy-equivalent secondary batteries; and have a low self-discharge rate. Nickel-Metal Hydride (NiMH) — Nickel-metal hydride batteries (secondary cells) are related to sealed nickel-cadmium batteries. The only difference is that instead of cadmium, hydrogen is used as the active element at a hydrogen-absorbing negative electrode (anode). This electrode is made from a metal hydride (usually alloys of lanthanum and rare earths) that serves as a solid source of reduced hydrogen that can be oxidized to form protons. The electrolyte is alkaline potassium hydroxide. The energy density of NiMH batteries is more than double that of lead acid. • Ultracapacitors (UltraCaps) — High-capacity electrochemical double-layer capacitors consisting of two electrodes immersed into an electrolyte. The electrodes are typically made of activated carbon which has a high, specific surface area of about 2,000 m2/g. UltraCaps have an unusually high energy density when compared to common capacitors, typically thousands of times greater than a high-capacity electrolytic capacitor.
- Environmental Protection Agency (EPA)
- A U.S. government agency established in 1970 to consolidate a variety of federal research, monitoring, standard-setting and enforcement activities to ensure environmental protection. The EPA’s mission is to protect human health and to safeguard the natural environment. Visit www.epa.gov to learn more. SmartWaySM Transport — A collaboration between the EPA and the freight sector designed to improve energy efficiency, reduce greenhouse gas and air pollutant emissions, and improve energy security. Visitwww.epa.gov/smartway/transport to learn more.
- E-PTO (Electric Power Take-off)
- An electric auxiliary drive used to power vehicle-mounted equipment instead of using power from the vehicle’s primary engine.
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- FH (Frame Height)
- The distance from the top of the frame to the ground. See Chassis Dimensions.
- Fifth Wheel
- A coupling device mounted on a tractor that contains a provision for accepting and holding the kingpin of a semi-trailer.
- Final-stage Manufacturer
- A person who performs such manufacturing operations on an incomplete vehicle that it becomes a completed vehicle.
- Abbreviation for Federal Motor Carrier Safety Regulation, regulations enforced by the Office of Motor Carrier Safety. See OMCS.
- Abbreviation for Federal Motor Vehicle Safety Standard. These regulations promulgated by the National Highway Traffic Safety Administration under Public Law 89-563 are mandatory and must be complied with when motor vehicles or items of motor vehicle equipment are manufactured and certified thereto.
- A device attached to the lift bar for lifting a vehicle by an axle, frame or structural member.
- Forward Control
- A configuration in which more than half of the engine length is rearward of the foremost point of the windshield base and the steering wheel hub is in the forward quarter of the vehicle length.
- Frame Cutoff
- The standard frame on most models extends behind the rear axle, far enough to support a body mounted on the vehicle. For special-purpose bodies that may be unusually short for the wheelbase of the vehicle on which it is mounted, or in most tractor operations this frame extension behind the rear axle may be shortened. The shortest allowable extension for each vehicle is referred to as Maximum Frame Cutoff.
- Frame Section Modulus
- The engineering term that indicates the relative strength of frames as it relates to shape. It takes into account frame depth, flange width and material thickness. All other things being equal, the frame with the largest section modulus will have the greatest strength and stiffness, (i.e., the ability to more effectively resist sagging under loads).
- Fuel Cell
- A device that generates electricity via a chemical reaction between a fuel (typically hydrogen) and oxygen. Every fuel cell has two electrodes, the anode (positive) and the cathode (negative). The reactions that produce electricity occur at the electrodes. Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes.
- Full Air Brakes
- Compressed air is used to provide the force required to expand the brake shoes by cam or wedge against the brake drums. Air pressure is supplied direct to chambers at the wheel position.
- Full Trailer
- A trailing load-carrying vehicle that is entirely supported by its own suspension system. The powered unit merely tows this type of trailer and does not directly support any of its weight. Sometimes referred to as a Pup when towed behind a truck with a mounted body or behind a tractor/semi-trailer combination. Tractor/semi-trailer/full-trailer combinations are often referred to as Doubles or Double Bottoms.
- FW (Frame Width)
- The overall width of the chassis frame measured outside to outside behind the cab.
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- Abbreviation for Gross Axle Weight Rating. The value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system, as measured at the tire-ground interfaces.
- Abbreviation for Gross Combination Weight Rating. Represents the entire weight of a vehicle at the ground with a trailer or trailers including vehicle, equipment, driver, fuel and payload (everything that moves with the vehicle.)
- Gear Ratio
- The number of revolutions a driving gear requires to turn a driven gear through one complete revolution. For a pair of gears, the ratio is found by dividing the number of teeth on the driven gear by the number of teeth on the driving gear.
- Geared Speed
- The theoretical vehicle speed based on engine RPM, transmission gear ratio, rear axle ratio and tire size.
- Glad Hand
- The air brake connector between a tractor and trailer.
- Grab Hook
- Device for use with safety chains and some tow hookups.
- Ability of a truck to negotiate a given grade at a specified Gross Vehicle Weight or Gross Combination Weight.
- Green Manufacturing
- A method of manufacturing that minimizes the use of non-renewable energy and resources as well as reduces the production of waste and pollution.
- Green Truck
Any truck that:
• When operated, significantly reduces the production of waste, pollutants and greenhouse gases;
• Increases productivity, resulting in a total reduction in fuel use to accomplish a given amount of work; or
• Has been manufactured using green materials and processes.
- Green Truck Association (GTA)
- An NTEA affiliate division that promotes the growing interest and demand for green products within the work truck industry. Learn more atwww.greentruckassociation.com.
- Abbreviation for Gross Vehicle Weight Rating. The maximum total vehicle weight, measured at the tire-ground interfaces, for which the vehicle possesses components adequately rated to safely carry. It cannot exceed the sum of all GAWRs.
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- Helical Gears
- Gears with slanted teeth, usually used in transmissions. The teeth are positioned diagonally across the face of the gear.
- Mechanism for elevating bodies, either level or tilting.
- Hold-over Plates
- Plate coils containing a refrigerant that are mounted on the walls of a truck or trailer. When "charged"; these plate coils hold the temperature down to the desired point for milk delivery and many other low-temperature trucking operations.
- Horizontal Center of Gravity (HCG)
- The point at which half of the gross weight is forward and half is aft. See Also Center of Gravity
- Horsepower (Gross)
- Obtained by dynamometer test of an engine with water pump(s) operating and air cleaner, but without generator, fan and muffler.
- Horsepower (Net)
- Obtained by dynamometer test of a complete engine with all standard accessories including water pump(s), generators and fan operating, air cleaner and muffler.
- Horsepower: Net
- Obtained by dynamometer test of a complete engine with all standard accessories including water pump(s), generators and fan operating, air cleaner, and muffler.
- Horsepower: Taxable
- The National Automobile Chamber of Commerce (NACC) adopted an arbitrary formula for estimating horsepower to enable comparison of engines on a uniform basis. It assumes that engines deliver their rated power at a piston speed of 1,000' per minute and that mechanical efficiency will average 75%. Advancements in engine design since this formula was developed have made the formula obsolete completely as a basis of estimating true engine output. However, the formula is still used in some states for licensing purposes.
- Hotchkiss Drive
- A term applied to that type of chassis design where the rear springs are mounted at the forward end in a stationary bracket (not shackled as at the read end) and all driving and braking forces are cushioned by the springs and transferred directly to the frame side members. Open-type universal joints and propeller shafts are used in this design.
- Hotel Loads
- Power demands (loads) placed on a vehicle to help maintain cab environmental conditions, such as heating, cooling, lighting and accessories (e.g., radios).
- Hybrid (Work Truck)
The combination of two different drive systems (conventional and alternative) to increase efficiency and reduce fuel consumption. Types of hybrids include:
• Electric Hybrid — A hybrid drive system that uses one or more electric motors, in parallel or series configuration, as the alternative drive system. Electric hybrids typically use batteries or ultracapacitors to store energy which is generated onboard the vehicle by the conventional engine and through regenerative braking.
• Hydraulic Hybrid — A hybrid drive system that uses one or more hydraulic motors, in parallel or series configuration, as the alternative drive system. Hydraulic hybrids typically use accumulators to store energy which is generated onboard the vehicle by the conventional engine and through regenerative braking.
• Hydraulic Launch Assist™ (HLA) — A hydraulic hybrid regenerative braking system introduced by Eaton Corporation. The HLA system recycles energy by converting kinetic energy into potential energy during deceleration via hydraulics, storing the energy at high pressure in an accumulator and returning it to the vehicle during subsequent acceleration. This process reduces the amount of work performed by the internal combustion engine.
• Parallel Hybrid — A hybrid drive designed so that either system can propel the vehicle independently or in unison.
• Plug-in Electric Hybrid (PHEV) — A variation of an electric hybrid that can charge the onboard energy storage system by plugging into the electric grid when the vehicle is not in use. Plug-in hybrids typically have greater onboard electric storage capacity than regular electric hybrids.
• Series Hybrid — A hybrid drive system designed so that only one system (normally the alternative) provides power to propel a vehicle. The conventional power source is used to provide energy to the alternative drive.
- Hydraulic Control Valve
- A mechanical device to divert or control the flow of fluid in a hydraulic circuit.
- Hydraulic Hose
- Flexible oil lines used to transmit fluid.
- Hydraulic Oil
- Fluid used to transmit power for operation for hydraulic systems.
- Hydraulic Relief Valve
- A mechanical device used to limit the pressure in a hydraulic circuit.
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- Abbreviation for Interstate Commerce Commission, the federal agency that regulates entry, rates, services, and insurance requirements for motor carriers, railroads, bus lines, freight forwarders, brokers, and waterway operators.
- Identification Lights
- Lighting cluster to indicate type of motor vehicle.
- Incomplete Vehicle
- An assemblage consisting, as a minimum, of frame and chassis structure, power train, steering system, suspension system, and braking system, to the extent that those systems are to be part of the completed vehicle that requires further manufacturing operations other than the addition of readily attachable components such as mirrors or tire and rim assemblies or minor finishing operations such as painting, to become a complete vehicle.
- Incomplete Vehicle Manufacturer
- A manufacturer that produces an incomplete vehicle (chassis) by assembling components none of which, if taken separately, constitutes an incomplete vehicle.
- Inside Height
- Unobstructed inside loading height measured at the side of a van body.
- Inside Safety Release
- A device mounted on the inside of a door to allow emergency exit if the door is accidentally locked from the outside.
- Inside Width
- Unobstructed inside loading width of a van body.
- Insulated Van Body
- A van body designed primarily for transportation of commodities at controlled temperatures. See Also Reefer
- Inter-axle Differential
- Sometimes called a Torque Divider Differential, this device is located between two driving axles of a tandem axle drive truck or tractor. The power from the engine is divided between the two driving axles when this device is in the unlocked position. One axle can actually turn faster, or at a different speed, than the other, which is an advantage in certain types of truck use. This device can be locked, under which condition both axles turn at exactly the same speed, getting approximately 50% of the power to each.
- Intermediate Manufacturer
- A person, other than the incomplete vehicle manufacturer or the final-stage manufacturer, who performs manufacturing operations on a vehicle manufactured in two or more stages.
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- Attachment device used for towing/recovery.
- Abbreviation for Joint Industry Committee, an organization set up to standardize hydraulic fittings specifications and symbols.
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- Kingpin-For Front Axle
- Pin that connects the front axle and steering spindle, about which the spindle pivots.
- Kingpin-For Semi-trailer
- Pin that is locked into the fifth wheel on a tractor to effect coupling of a trailer with the tractor.
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- LA (Load-to-Axle)
- The distance from the center of gravity (CG) of the body and or payload to the center line of the rear axle(s). See Also Chassis Dimensions
- Landing Gear
- A structure used to support the front of a semitrailer when detached from a tractor.
- A financial arrangement that merely provides the vehicles; the fleet company must provide maintenance and insurance and pay for depreciation.
- Abbreviation for “Light Emitting Diode,” a semi conductor diode that converts applied voltage to light and is used in digital displays.
- A company that has obtained vehicles by leasing them.
- A leasing company.
- Lift Bar
- A transverse horizontally pivoting member attached to the boom of a wheel lift or an underlift for attaching frame or wheel-lift devices. Also called Cross Bar.
- Lift Gate
- See Elevating Gate.
- Lift-tow Rating
- Rating of a wrecker or recovery vehicle that gives the maximum weight of a vehicle to be towed.
- Light Bar
- An array of lamps used in accordance with local ordinances.
- Light Pylon
- Structure upon which a light and or light bar is mounted.
- Lightly Loaded Vehicle Weight
- (1) For vehicles with a GVWR of 10,000 lbs. or less, unloaded vehicle weight plus 300 lbs. (including driver and instrumentation); (2) For vehicles with a GVWR greater than 10,000 lbs., unloaded vehicle weight plus 500 lbs. (including driver and instrumentation). This weight is used for EPA testing and compliance.
- See Clearance Lights, Identification Lights and Marker Lights.
- Light-truck Tire
- A tire designated by its manufacturer as primarily intended for use on lightweight trucks or multipurpose passenger vehicles.
- Load Cell
- A device used to measure a load.
- Body members attached to and running the length of an underframe. Also called Longrails, Longsills, Risers, or Stringers.
- See Longitudinal.
- Lower Rail
- Lower framing member of front, sides, and occasional rear sections of a van body.
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- Maintenance Lease
- Sometimes called Fix Cost Leasing. The leasing company provides insurance and all maintenance and covers depreciation.
- Individual company engaged in the manufacturing or assembling of motor vehicles or motor vehicle equipment, including any party importing same, for resale as defined by the DOT for vehicle certification.
- Marker Lights
- Amber and red lights attached to the vehicle body which indicate overall length.
- Maximum Load Rating
- The load rating at the maximum permissible inflation pressure for that tire.
- Maximum Loaded Vehicle Weight
- The sum of curb weight, passengers, and cargo.
- Maximum Permissible Inflation Pressure
- The maximum cold inflation pressure to which a tire may be inflated.
- Maximum Rolling Grade (Gradeability)
- Greatest grade a vehicle is able to climb while under motion.
- Maximum Speed
- The speed attainable by accelerating at maximum rate from a standing start for one mile.
- Maximum Starting Grade (Gradeability)
- Greatest grade on which a vehicle is able to start from a complete stop. Approximately 9 10ths of Rolling Gradeability.
- Maximum Sustained Vehicle Speed
- Highest speed a vehicle can maintain under full load conditions on level ground.
- Monocoque Construction
- A light weight type of construction, commonly utilized in van type semitrailers, where the sides of the vehicle bear a substantial part of the load in shear which is transmitted to the upper coupler and undercarriage assemblies through side rails, crossmembers and end structures.
- Mounting Devices
- Usually U bolts, tie down clamps, and or straps to secure a van body to a chassis cab. Also referred to as Mounting Brackets, Mounting Clamps, Angles, or Bars.
- Mounting Height
- Distance from top of chassis cab frame to bottom of body floor.
- Mounting Subframe
- Subframe members securely affixed to a truck chassis frame.
- Mud Flap
- Deflecting shield at rear of wheels, required by regulation. Also called Splash Guard. See Splash Guard.
- Multifunction School Activity Bus (MFSAB)
- Means a school bus whose purposes do not include transporting students to and from home or school bus stops.
- The process of transmitting several different signals or information streams via a single carrier. This occurs by combining the signals into one common signal that efficiently moves through the carrier.
- Multipurpose Passenger Vehicle (MPV)
- Means a motor vehicle with motive power, except a low-speed vehicle or trailer, designed to carry 10 persons or less which is constructed either on a truck chassis or with special features for occasional off-road operation.
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- National Truck Equipment Association (NTEA)
- Established in 1964, the NTEA is the leading association for the work truck industry, offering expert knowledge, technical support, strategic resources and business opportunities. The Association represents nearly 1,600 companies that manufacture, distribute, install, buy, sell and repair commercial trucks, truck bodies, truck equipment, trailers and accessories. Many buyers of work trucks (fleets) and the major commercial truck chassis manufacturers also belong to the NTEA.
- Abbreviation for National Highway Traffic Safety Administration, the federal agency responsible for promulgating and ensuring compliance of regulations dealing with the manufacture and certification of motor vehicles. See DOT.
- Nominal Rating
- An arbitrary classification of truck capacity in tons, such as: half-ton, three-quarter ton, one ton, ton and a half, two tons, five tons, etc.
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- Overall length of a vehicle. See Also Chassis Dimensions
- Occupational Safety and Health Administration (OSHA)
- The federal agency that promulgates and ensures compliance of regulations dealing with on-the-job safety and health. Some motor vehicle regulations are included that apply to vehicles used in off-highway job sites. Compliance is the responsibility of the vehicle owner.
- A mileage counter that registers total miles traveled. Located on the dial section of most speedometers.
- Slow speed operations over uneven surfaces such as lumbering operations, oil field work, geological surveying, operations at mining sites, road construction and other major construction sites.
- Abbreviation for Office of Motor Carrier Safety, an office of the Federal Highway Administration within the Department of Transportation. Responsible for developing and implementing national motor carrier standards and intermodal hazardous materials regulations and issuing interpretations and reviewing state laws and regulations.
- Operations mostly on hard surfaced or graded roads with some work over unprepared surfaces. In this category are most highway units not operated over regular routes such as farm trucks, dump trucks, concrete mixers, lumber delivery, trucks, etc.
- Open Top
- A body without a permanent top assembly.
- Abbreviation for Occupational Safety and Health Administration, the Federal agency which promulgates and ensures compliance of regulations dealing with on the job safety and health. Some motor vehicle regulations are included that apply to vehicles used in off
- Folding or sliding leg devices attached to trucks to give additional support down to the ground for maximum stability.
- Overall Vehicle Height
- Distance from the ground to the highest point on the vehicle.
- Overall Vehicle Width
- Refers to the nominal design dimension of the widest part of the vehicle, exclusive of signal lamps, outside rearview mirrors, flexible fender extensions and mud flaps, determined with doors and windows closed and the wheels in the straight-ahead position.
- (a) The horizontal distance from the center line of the hinge to the rear of the body on a tilting body (b) The distance from the center of the rear axle(s) to the rearmost surface of the truck body. Usually applies to nontilting bodies.
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- Parallel Batteries
- All batteries have their positive terminals connected on a separate wire and all negative terminals on another separate wire. This means that four six-volt batteries (some trucks carry four batteries) will still produce only six volts, but will have four times the energy potential.
- The weight of the commodity being hauled. Payload capacity is computed by subtracting the completed weight of the vehicle (including driver and passengers) from the GVWR.
- Payload &Body Allowance
- The payload capacity of the truck with allowance for the weight of a truck body.
- Peddle Truck or Shuttle Truck
- Terms for the city delivery trucks owned by a long-distance hauler. They distinguish between the big “rigs” and the small city trucks.
- Percent of Grade
- The figure used in computing the power requirements of a truck. Usually taken at the steepest grade a truck will be required to climb on its route. Percent of grade is determined by dividing the height of a hill by its length.
- Pintle Hook
- Hook mounted on a truck or semi-trailer used to couple a full trailer.
- Pitch Line Velocity (PLV)
- The circumference in feet at the pitch line of a gear multiplied by the RPM of that gear at 1,000 engine RPM. A small PTO driving gear in the transmission gives a low pitch line velocity; a larger gear gives a correspondingly higher pitch line velocity.
- Load-carrying bed with or without removable sides. May be equipped with hydraulic cylinders to tilt and slide platform.
- Ply Rating
- A standard unit of tire casing strength, based on the strength of cotton plies. This term is used to indicate the load-carrying ability of a given tire. It is an index of tire strength and does not necessarily represent the number of cord plies in the tire.
- Pole Trailer
- A motor vehicle without motive power designed to be drawn by another motor vehicle and attached to the towing vehicle by means of a reach or pole, or by being boomed or otherwise secured to the towing vehicle. Used for transporting long or irregularly shaped loads such as poles, pipes or structural members generally capable of sustaining themselves as beams between the supporting connections.
- Power Curve
- A graphic illustration of maximum output of horsepower and torque at all operating speeds. These curves are established from data obtained by running a sample engine on an engine dynamometer. Curves are established using bare operable engine and with standard accessories. Net power figures (those using standard accessories) are used in vehicle performance calculations.
- Power Divider
- Usually a small auxiliary gear box or chain-driven device to allow distribution of drive shaft power to several different mechanical devices mounted on the same truck.
- Power Take-off (PTO)
- A mechanical device used to transmit engine power to auxiliary equipment. Power take-offs can be mounted on either a main or auxiliary transmission. Front-mounted and flywheel-mounted power take-offs are also used in various applications.
- Power Train
- All the components that handle the engine power from the truck engine to the driving wheels. This includes transmissions, drive shafts, as well as differentials and driving axles.
- Private Fleet
- A truck fleet owned for a company’s own use.
- Push Bumper
- Device used to push a vehicle, sometimes equipped with a rubber face.
- Pusher Axle
- An auxiliary axle installed in conjunction with the rear axle(s) of a truck chassis. A pusher axle is installed ahead of the drive axles, thus shortening the length of the wheelbase.
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- Radius Rod
- Found in several automotive applications, most commonly for keeping the rear axle in correct position when starting and stopping.
- Rear Axle Ratio
- The numerical ratio of the drive shaft speed to the speed of the rear axle.
- Recovery Vehicle/Wrecker
- Vehicle used to retrieve and lift tow other vehicles.
- Slang for insulated van body equipped with refrigeration for controlling temperatures.
- Glass or plastic prism lenses which reflect light.
- Regrooved Tire
- A tire, either original tread or retread, on which the tread pattern has been renewed or a new tread has been produced by cutting into the tread of a worn tire to a depth equal to or deeper than the molded original groove depth.
- Resisting Bending Moment (RBM)
- A calculation used to compare frames of different section modulus and of different material. It is the product of the section modulus times the yield strength of the frame material. The formula is expressed as:
- RBM = Section Modulus x Yield Strength
- It is readily apparent from the above formula that the yield strength of a frame is as important as the section modulus. The RBM should, therefore, be taken into account whenever frames of unlike material and section modulus are being compared. See Yield Strength.
- Ridge Pole
- Member that can be located in center longitudinally on an open top van body to support a tarpaulin in a tent like manner.
- Rim Pull
- See Tractive Effort.
- Steel or wood section between chassis frame and van body underframe to give proper tire clearance and/or required ground-to-floor height.
- Road Rolling Resistance
- A measure of the retarding effect of the road surface to forward movement of the vehicle. Varies with the type and condition of the road as different road surfaces offer various resistances to the wheels of a truck. A concrete surface offers 12.5 lbs. of rolling resistance per thousand pounds of gross weight; gravel, 25 lbs.; and sand, 75 lbs. This is a vital factor in determining power and power train requirements.
- The left or driver’s side of the vehicle when viewed from the rear, opposite side from Curbside.
- Rolling Radius
- Height measured from center of axle to the ground.
- Roof Bow
- Transverse member in roof of body.
- Roof Rail
- Member running longitudinally that connects the roof to the side of a body.
- Rope Ties
- Rings, hooks, cleats or knobs attached to body wall frame members for use with lashing either inside or outside; liner slats or bars attached to wall frame members for lashing.
- Rub Rail
- Member running longitudinally providing rub surface on the side of a body.
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- Abbreviation for Society of Automotive Engineers.
- Safety Chains
- Chain assemblies used to connect the towing and towed vehicles as a secondary coupling system.
- School Bus
- A bus that is sold or introduced in interstate commerce for purposes that include carrying students to and from school or related events. Does not include a bus designed and sold for operation as a common carrier in urban transportation.
- School Bus Passenger Seat
- A seat in a school bus other than the driver’s seat.
- Self Regeneration System
- An onboard system that converts a hybrid vehicle’s kinetic energy (energy of motion) into potential energy (stored electricity or high-pressure hydraulic fluid) during deceleration or braking (regenerative braking). This energy is then returned to the drive system during subsequent operations.
- A trailing unit that is supported in the rear by its own suspension system and at the front by the towing vehicle. This type of unit is sometimes supported by a separate suspension unit with towing provisions (thus becoming a full trailer). An exception is the utility-type trailer, house trailer, etc. that is towed by a ball coupling (referred to simply as a trailer and is not designed as semi- or full trailer).
- Serial Number
- A number stamped on a metal plate by the manufacturer and placed on a component or the vehicle for identification purposes. See Vehicle Identification Number (VIN).
- Set-back Front Axle
- The front steering axle is normally as close to the front of the vehicle as the design and wheel and tire size permit. When the front axle is purposely located farther toward the rear, it is referred to as being “set back.” Center line of front axle to front of front bumper is normally from 28" to 37" on regular models and 48" or more on set-back front-axle models. The purpose of moving the axle rearward is to increase loads applied to the front axle and increase maneuverability. Standard type front-axle setting generally enables more economical cab construction and meets axle spread requirements of states using the Bridge Formula.
- Shipping Weight
- The dry weight of a complete truck with all standard equipment including grease and oil but without any fuel or coolant.
- Short Chain
- Method of attaching a tow sling to a towed vehicle so that the tow chains support the entire load.
- Side Rails
- Upper or lower extensions of the body sides that run longitudinally, front to back.
- Single & Double Reduction Gears
- Generally rear-axle terminology. Standard rear-axle gearing is single reduction, (i.e., one step of speed reduction through the rear-axle gearing). In certain heavy-duty applications a double reduction is desirable. This permits a greater gear reduction in a smaller gear case, thus allowing better road clearance and more compact design.
- Slideback Cylinder
- A hydraulic cylinder, usually a long stroke, mounted horizontally at front of body used to slide body forward or rearward.
- Snatch Block
- A single or multiple pulley used to reduce cable load or change cable direction.
- Steel or wood section between chassis frame and body underframe to give proper tire clearance and/or required ground-to-floor height.
- Spacer Block
- Used in conjunction with 4x4 wood beam to provide additional clearance between the tow bar, chains and body of the vehicle.
- One or more hydraulically operated ground-penetrating feet designed primarily to resist rearward movement.
- The speed a vehicle will attain based on engine power, gross weight, power train efficiency, air resistance, grade resistance and road type.
- Splash Guard
- See Mud Flap.
- Spring Capacity
- (1) Capacity at Pad: The total weight that the spring can support in its maximum position; (2) Capacity at Ground: The total weight that the spring can support in its maximum position plus a portion of the weight not supported by the springs.
- Hydraulic or manually operated leg devices attached to trucks to give additional support down to the ground for improved stability. Examples are outboard legs, outriggers and jack legs.
- Stake Pockets
- Apertures in the floor or sides of bodies for the reception of stakes.
- Metal or wood posts by means of which sides are attached to platforms; when used alone stakes are a means of retaining loads on flat deck platforms.
- Steering Wheel Lock
- Independent device used to secure the steering wheel of a towed vehicle.
- Stationary Lighting Loads
- Vehicle electrical loads that provide lighting on stationary vehicles for work area protection or safety (e.g., flashers and strobe lights) and interior and exterior work area lighting.
- Steering Wheel Lock
- Independent device used to secure the steering wheel of a towed vehicle.
- Stopping Distance
- The distance traveled by a vehicle from the point of application of force to the brake control to the point at which the vehicle reaches a full stop.
- (1) In engines, the distance traveled by a piston from top dead center to bottom dead center; (2) Maximum distance traveled by the piston in an air or hydraulic cylinder.
- Sub Pan
- Horizontal surface installed either between or above crossmembers prior to insulation and installation of flooring in reefers.
- Suction Line
- A tubular connection between a reservoir or tank and the inlet of a hydraulic pump.
- Supply Tank
- An oil reservoir used in the hydraulic system.
- The use of methods, systems and materials that minimize or avoid resource depletion and harm to natural cycles.
- Swing Axle
- A drive axle arrangement found on some passenger cars and some light-duty trucks. The differential is mounted rigidly on the vehicle frame and the axle shafts are allowed to “swing” as the vehicle moves up and down while running. Lower unsprung weight is one advantage of this system. Universal joints are required on each half of the drive axle to accommodate the vertical motion.
- Synchronized or Synchromesh Transmission
- A truck transmission with built-in devices to automatically match the rotating speeds of the transmission gears. With this type of transmission, “double clutching” is not necessary.
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- An instrument that indicates the revolutions per minute (RPM) of the engine.
- Tag Axle
- An auxiliary axle installed in conjunction with the rear axle(s) of a truck chassis. A tag axle is installed behind the rearmost axle, thus extending the length of the wheelbase. See Tandem Axle.
- Tail Plate
- Rearmost part of the towing or recovery vehicle body.
- Tandem Axle
- Two axles mounted as a group (three axles placed together are often referred to as a Tri-axle Tandem). There are three tandem-axle drive types: (1) Dual-drive Tandem, both axles have drive mechanisms and are connected to the engine power unit; (2) Pusher Tandem, only the rearmost axle is a driving type and forward unit is free rolling (load-carrying only), commonly called Dead Axle; (3) Trailing Axle Tandem (Tag Axle), forward unit of tandem is a driving type while rear unit is freely rolling. Two trailer axles are also called tandem axles.
- Tare Weight
- The total weight of an empty vehicle in a condition ready to receive payload. Same as Curb Weight.
- The integrated use of telecommunications and informatics, also known as Information and Communications Technology (ICT). More specifically, telematics is the science of sending, receiving and storing information via telecommunication devices, including cellular communications and satellite systems.
• Active Telematics —Systems that are typically capable of interfacing with a vehicle on a real-time basis.
• Passive Telematics —Systems that may send or receive information but cannot actively interface with a vehicle.
- Thermal Efficiency
- The efficiency of an engine in converting heat energy from combustion of fuel into mechanical work.
- Attachment device used for towing.
- Tiedown Assemblies
- Device(s) used to restrain cargo. Also called Cargo Control or Restraint Equipment.
- Tilt Cab
- Vehicle designed with engine beneath cab and having provision for tilting cab forward on a pivot near front bumper to provide easy access to engine.
- Tilt Cylinder
- Cylinders used to change the attitude of a structure or body.
- Tire Clearance
- Space between tires and nearest part of the body or under-construction.
- Tire Loaded Radius
- The distance from the center of the wheel to the road with tire loaded to rated capacity. Static radius applies when vehicle is at rest; rolling radius for a vehicle when in motion. The latter dimension is usually slightly greater than the static radius and is the figure used in determining the tire revolutions per mile.
- The rotating or twisting force developed by the truck engine. This is one of the two factors in figuring horsepower and is always expressed in pound-feet. At a given RPM, the higher the torque, the greater the horsepower. The higher the torque rating of a truck engine, the greater its ability to climb hills and increase speeds. A high-torque truck engine eliminates a lot of gear shifting for the driver.
- Torque Converter
- Used in truck and car automatic transmissions. Torque is multiplied by the action of various turbine-like elements on a fluid.
- Torque Multiplication
- The truck transmission as well as rear-axle gears multiplies the engine’s torque. This is done by reducing engine speed through gears, thus increasing torque by reducing revolutions per minute.
- Tow Bar
- A device for positioning a towed vehicle behind a recovery vehicle.
- Tow Chains
- Chain assemblies used as a primary coupling between towing and towed vehicles (not the same as Safety Chain).
- Tow Sling
- A device used for lifting and towing vehicles with the load supported on rubber belts and chains.
- Tow Vehicle
- Vehicle used to lift/tow other vehicles.
- Tractive Effort
- The force available at the road surface contacting the driving wheels of the truck. Determined by engine torque, transmission ratio, axle ratio, tire size and frictional losses in the driveline. Also called Rim Pull.
- Tractive Factor or Performance Factor
- This is tractive effort per thousand pounds of gross vehicle weight. A means of measuring the performance potential of a truck or tractor.
- A truck of comparatively short wheelbase used for pulling a semi-trailer.
- Tractor Breakaway Valve
- Coupled between the tractor and trailer emergency brake system, the tractor breakaway valve provides an air supply to the trailer emergency system for normal operating conditions. In case of trailer brake system failure, the breakaway valve automatically seals off the flow of air pressure from the tractor to the trailer preventing the loss of air pressure from the tractor braking systems and activates the trailer emergency brake. In conjunction with a breakaway valve, a dash-mounted manual control valve is located in the cab. This manual control is used to charge the trailer brake system reservoir for normal operation. In the event of loss of air pressure in the normal braking system, this manual control can be used to seal off the tractor brake system.
- A motor vehicle with or without motive power, designed for carrying persons or property and for being drawn by another motor vehicle.
- Trailer Converter Dolly
- A trailer chassis equipped with one or more axles, a lower half of a fifth wheel and a drawbar.
- A gear reduction device that contains an assembly of gears and associated parts that transmits power from the engine to the driving axle(s). A transmission contains a number of gears that when a connection is made between a specific set provides a choice of ratio. Connection is made by sliding the teeth of one gear into mesh with another, or by engaging a tooth-type clutch that has one part fastened to a gear already meshed to another and the other part splined to a shaft. Synchromesh transmissions use gear-speed synchronizers to ease engagement.
- (1) The distance between the centers of tires on the same axle at the points where they contact the road surface. Duals are measured from the center of dual wheels; (2) That portion of a tire that comes into contact with the road.
- Tread Rib
- A tread section running circumferentially around a tire.
- Tread Separation
- Pulling away of the tread from the tire carcass.
- A motor vehicle with motive power, except a trailer, designed primarily for the transportation of property or special purpose equipment.
- Truck Hitch
- A device for positioning and supporting one end of a towed vehicle behind a recovery vehicle.
- Truck Tractor
- A truck designed primarily for pulling a semi-trailer and not so constructed as to carry a load other than a part of the weight of the semi-trailer. See Tractor.
- The axis, pivot point or center point between axles. A Trunnion Bar is used in single-point tandem suspensions.
- Turning Radius
- The shortest distance in feet required for a given truck to negotiate a U-turn or make a 180-degree turn. The smaller the turning radius of the truck, the greater its maneuverability and consequent ability to handle well in heavy traffic or congested areas.
- Twin Screw
- Slang term for Tandem Drive.
- Two-speed Axle
- A rear axle arrangement whereby the driver can select one of two ratios. A truck with a two-speed axle and a five-speed transmission would have 10 forward speeds.
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- A device used for towing vehicles by lifting one end of the towed vehicle from under the axle or structural member.
- Universal Joint
- Truck drive shafts have universal joints to allow for vertical motion of drive axle and change of angle due to truck loading. Universal joints are used wherever a drive or control shaft must have a change of angle along its axis.
- Unloaded Vehicle Weight
- The weight of a vehicle with maximum capacity of all fluids necessary for operation of the vehicle, but without cargo, occupants or accessories that are ordinarily removed from the vehicle when they are not in use.
- Unsprung Weight
- All the vehicle weight that is not supported by the truck’s springs, including wheels, tires, brakes, axles and drive shaft. The objective of design engineers is to reduce unsprung weight to a practical minimum.
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- Abbreviation for Vertical Center of Gravity, the point at which half of the gross weight is above and half is below. See Center of Gravity.
- Vehicle Equipment Safety Commission
- The Commission established pursuant to the joint resolution of the U.S. Congress relating to highway traffic safety, approved Aug. 20, 1958 (72 Stat. 635), or as it may be hereafter reconstituted by law.
- Vehicle Identification Number (VIN)
- A 17-character number consisting of arabic numerals, roman letters, or both, that the manufacturer assigns to a vehicle for identification purposes, as required by 49 CFR Part 565.
- Vehicle Maximum Load on the Tire
- That load on an individual tire that is determined by distributing its share of the maximum loaded vehicle weight to each axle and dividing by two.
- Volumetric Efficiency
- The ratio of air inducted per cycle to the total displacement of the engine. Commonly referred to as the engine’s ability to “breathe.”
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- Walking Beam Suspension
- Term used to describe a type of tandem suspension that has equalizing beams connecting the two axles. In a parallelogram design such as this, wheels “walk” over irregularities in the road surface.
- Weight Distribution
- The distribution of the total gross vehicle weight imposed on the ground at each axle (measured in units of weight or as a percent of total truck weight).
- The weight of those things supported by the springs, such as frame, engine, body, payload, etc.
- Wheel Arm
- A device that attaches to the lift bar for engaging the tires of a towed vehicle.
- Wheel Lift
- A device used for towing vehicles by lifting one end of the towed vehicle from under the tires.
- Wheel Straps
- Used to tie down wheels when using wheel-lift or dolly tow equipment.
- Wheelbase (WB)
- Horizontal dimension from the center line of the front axle to the center line of the rear axle on a single-rear-axle truck chassis; measured from the center line of the front axle to the center line mid-way between the axles on a tandem-rear-axle truck chassis. See Chassis Dimensions.
- Housing over wheels replacing floor area to obtain lower floor loading height or lower mounting height.
- Housings in body floor to allow clearance over tires.
- A device for winding and unwinding a cable under power.
- Working Limit
- Minimum breaking strength divided by the factor of safety for cable or chain.
- Truck equipped with winch or winches and boom(s) used for recovering and towing vehicles. Term may be used to also mean only the equipment not including the truck chassis.
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- Yield Strength
- The inherent strength of a material by indicating the maximum load that can be applied to that material before permanent deformation occurs. This means, in effect, the maximum load that will allow the material to return to its original shape when the load is removed.