| A - Back to Top |
| Above-cab Carrier
A platform above the cab which can be in a fixed or hydraulically adjustable position for transporting vehicles. |
| AF (Axle-to-Frame)
The distance from center of rear axle(s) to end of frame. See Also: Chassis Dimensions |
| Air Dam
Flexible air deflecting panel usually located below the radiator support. |
| Air Resistance
Glossary U.S. Federal Lighting Guide (FMVSS 108) Hoist Capacity Database Chassis Manufacturer Contacts ASE Certification Product Conference Industry Statistics Government/FET Business Resources Member Resources About NTEA Join NTEA Contact Us Feedback FREE Downloads FREE Newsletter Home / Technical Resources / Truck Equipment Glossary / Definition 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. |
| 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
(a) 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; (b) An angle made between the plane of the platform and the ground plane on a carrier body. |
| Auxiliary Equipment
Any equipment, in addition to the basic chassis, that is required for a piece of equipment/vehicle to perform its functions. For example, a winch would be auxiliary equipment for a tow truck. |
| Auxiliary Fuel Tanks
Fuel tanks installed in addition to the standard equipment tank. |
| 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. |
| AWG
Abbreviation for American Wire Gauge, a system that specifies wire size. The smaller the AWG number, the larger the wire diameter. |
| Axle Rating
See Gross Axle Weight Rating. |
| Axle: Dead
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. |
| Axle: Drive
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. |
| Axle: Live
A means of support for the wheels at each end that connects the wheels with members which rotate with the wheels. |
| Axle: Semifloating
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. |
| B - Back to Top |
| BA
The distance from the foremost point on the front bumper to the center line of the front axle. See Also: Chassis Dimensions |
| Baffle
A plate or shield used for deflecting, checking or regulating the flow of liquids or gases. |
| Barrel
The cylindrical component of the hydraulic cylinder. |
| Battery
An electro-chemical device for storing electrical energy. |
| BBC
The distance from the foremost point on the front bumper to the back of the cab. See Also: Chassis Dimensions |
| Bending Moment
The force times the distance from the support to the point the force is applied causing bending. |
| Bevel Gear
Gear which will transmit power at an angle. |
| BHP
Abbreviation for Brake Horsepower. See Also: Horsepower |
| BL (Body Length)
The distance from the foremost point of the body to the rearmost point of the body. See Also: Chassis Dimensions |
| Blower
A tank vehicle accessory (which may be either tractor-mounted or trailer-mounted) used in the transfer by air of dry bulk products at pressures normally below 5 psi. |
| Body
The structure or that portion of the vehicle which 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. |
| Bogie
A Tandem Axle. |
| Bolsters
The transverse members commonly used to define the horizontal support for the diagonal braces of a vertical mast. |
| Boom
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. |
| C - Back to Top |
| 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 Also: Chassis Dimensions |
| Cab
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. |
| Cable
Steel wire rope used for pulling or supporting. |
| Camber
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 Ibs. times the number of designated seating positions. |
| Carrier
A platform body with a winch for loading. |
| Caster
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 |
| CCA
Abbreviation for Cold Cranking Amps, a performance rating for automotive starting batteries. |
| CDL
Abbreviation for Commercial Driver's License. A license issued by a State or other jurisdiction, in accordance with the standards contained in 49 CFR Part, 383, to an individual which authorizes the individual to operate a class of a commercial motor vehicle. |
| 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 |
| Center of Gravity (CG)
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 are defined as follows: * (HCG) Horizontal: measured fore and aft from a reference plane * (LCG) Lateral: measured from center line of the vehicle to the side * (VCG) Vertical: measured up or down from a reference plane. |
| Certification Label
A label, required by Public Law 89-563, which states (certifies) that a motor vehicle or item of motor vehicle equipment complies to all applicable Federal Motor Vehicle Safety Standards (FMVSS) in effect on the date of manufacture. |
| Cetane
Rating of diesel fuel similar to octane for gasoline. |
| Chain Assemblies
Chain with all hardware and coupling devices. |
| Chassis Cab
An incomplete vehicle consisting of a chassis upon which is mounted a completed occupant compartment. The vehicle is capable of performing work by the addition of a body/load-carrying structure. |
| Chassis Dimensions
Designations commonly used to describe a truck and its components. See illustration below. AF = Axle to End of Frame BA = Bumper to Axle BBC = Bumper to Back of Cab BL = Body Length CA = Cab to Axle CB = Cab to Body CE = Cab to End of Frame FH = Frame Height LA = Load to Axle OAL = Overall Length WB = Wheelbase |
| 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. |
| CMV
Abbreviation for Commercial Motor Vehicle from the FMCSR Title 49 CFR, Part 390.5 that means any self-propelled or towed motor vehicle used on a highway in interstate commerce to transport passengers or property when the vehicle: 1. Has a GVWR or GCWR, or GVW or GCWR, of 4,536 kg (10,001 lbs.) or more, whichever is greater; or 2. Is designed or used to transport more than eight passengers (including the driver) for compensation; or 3. Is designed or used to transport more than 15 passengers, including the driver, and is not used to transport passengers for compensation; or 4. Is used in transporting material found by the Secretary of Transportation to be hazardous under 49 U.S.C. 5103 and transported in a quantity requiring placarding under regulations prescribed by the Secretary under 49 CFR, subtitle B, chapter 1, subchapter C. |
| 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. |
| Cowl
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. |
| Crossmembers
General term applied to transverse members in the understructure or on a truck frame. |
| CT (Cab-to-Tandem)
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. |
| Cube
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. |
| Curbside
The right or passenger side of the vehicle when viewed from the rear, opposite side from Roadside. |
| Cylinder
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. |
| D - Back to Top |
| 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. |
| Differential
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, standard equipment on some. |
| Displacement
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. |
| DOT
Abbreviation for Department of Transportation, the agency composed of several federal agencies dealing with regulations concerning both the manufacture and operation of motor vehicles and motor vehicle equipment. |
| Double-bottom or Tandem Trailer
A combination consisting of a tractor pulling a semitrailer with a full trailer in back. |
| Driveline
The total system drive shaft consisting of universal joints, slip yokes and flanges between the transmission and axle(s). |
| E - Back to Top |
| 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 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. |
| EPA
Abbreviation for Environmental Protection Agency, the federal agency which establishes and enforces regulations to protect the environment. These regulations include pollution of the air and water, as well as pollution from fuel and/or noise emissions. |
| F - Back to Top |
| FH (Frame Height)
The distance from the top of the frame to the ground. See Also: Chassis Dimensions |
| Fifth Wheel
A coupling device mounted on a tractor which contains a provision for accepting and holding the kingpin of a semitrailer. |
| Final-stage Manufacturer
A manufacturer that performs such manufacturing operations on an incomplete vehicle that it becomes a complete vehicle and road-ready for its intended purpose. |
| FMCS
Abbreviation for Federal Motor Carrier Standard, regulations enforced by the Office of Motor Carrier Safety. See Also: OMCS |
| FMCSR
Abbreviation for Federal Motor Carrier Safety Regulations enforced by the Federal Motor Carrier Safety Administration. |
| FMVSS
Abbreviation for Federal Motor Vehicle Safety Standard. These regulations promulgated by the National Highway Traffic Safety Administration (NHTSA) 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. |
| Forks
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. |
| 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 which 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-semitrailer combination. Tractor-semitrailer/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. |
| G - Back to Top |
| GAWR
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. |
| GCWR
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. |
| Gradeability
Ability of a truck to negotiate a given grade at a specified Gross Vehicle Weight (GVW) or Gross Combination Weight (GCW). |
| GVWR
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. |
| H - Back to Top |
| Helical Gears
Gears with slanted teeth, usually used in transmissions. The teeth are positioned diagonally across the face of the gear. |
| Hoist
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
The rate of doing work equal to lifting 33,000 Ibs. one foot in one minute; the amount of work done by a certain torque developed by an engine on a per-minute basis. |
| Horsepower: Brake (or Actual Delivered Horsepower)
A measure of the rate at which engine power is produced - the time rate of doing work, as measured by a Prony brake or an electric dynamometer. In other words, the amount of work done by a certain torque being exerted over a definite space of time. Brake horsepower is expressed as the torque in pound-feet times the number of revolutions per minute divided by the constant 5252. |
| 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 NACC (National Automobile Chamber of Commerce) 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 1000 feet per minute and that mechanical efficiency will average 75%. Advancements in engine design since this formula was developed have obsoleted the formula completely as a basis of estimating true engine output. The formula is still used in some states for licensing purposes, however. |
| 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. |
| 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. |
| I - Back to Top |
| ICC
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 manufacturer, other than the Incomplete Vehicle Manufacturer or the Final-stage Manufacturer, that performs manufacturing operations on an incomplete vehicle. |
| J - Back to Top |
| J-Hook
Attachment device used for towing/recovery. |
| JIC
Abbreviation for Joint Industry Committee, an organization set up to standardize hydraulic fittings specifications and symbols. |
| K - Back to Top |
| Kingpin, Front Axle
Pin that connects the front axle and steering spindle, about which the spindle pivots. |
| Kingpin: For Semitraile
Pin that is locked into the fifth wheel on a tractor to effect coupling of a trailer with the tractor. |
| L - Back to Top |
| 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. |
| Lease
A financial arrangement which merely provides the vehicles; the fleet company must provide maintenance and insurance and pay for depreciation. |
| LED
Abbreviation for "Light Emitting Diode," a semi-conductor diode that converts applied voltage to light and is used in digital displays. |
| Lessee
A company that has obtained vehicles by leasing them. |
| Lessor
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
(a) For vehicles with a GVWR of 10,000 Ibs. or less, unloaded vehicle weight plus 300 Ibs. (including driver and instrumentation); (b) For vehicles with a GVWR greater than 10,000 Ibs., unloaded vehicle weight plus 500 Ibs. (including driver and instrumentation). This weight is used for EPA testing and compliance. |
| Lights
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. |
| Longitudinal
Body members attached to and running the length of an underframe. Also called Longrails, Longsills, Risers, or Stringers. |
| Longrails
See Longitudinal. |
| Lower Rail
Lower framing member of front, sides, and occasional rear sections of a van body. |
| M - Back to Top |
| Maintenance Lease
Sometimes called Fix Cost Leasing. The leasing company provides insurance and all maintenance and covers depreciation. |
| Manufacturer
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, cross members, 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
See Splash Guard. |
| N - Back to Top |
| NHTSA
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 Also: 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. |
| O - Back to Top |
| OAL
Overall length of a vehicle. See Also: Chassis Dimensions |
| Odometer
A mileage counter that registers total miles traveled. Located on the dial section of most speedometers. |
| Off-Road
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. |
| OMCS
Abbreviation for Office of Motor Carrier Safety, an office of the Federal Highway Administration (FHWA) within the Department of Transportation (DOT). Responsible for developing and implementing national motor carrier standards and intermodal hazardous materials regulations and issuing interpretations and reviewing state laws and regulations. |
| On/Off-Road
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. |
| OSHA
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-highway job sites. Compliance is the responsibility of the vehicle owner. |
| Outriggers
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. |
| Overhang
(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 non-tilting bodies. |
| P - Back to Top |
| 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. |
| Payload
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 truck or semitrailer 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. |
| Platform/Flatbed
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 both 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. |
| R - Back to Top |
| Radius Rod
It's a Radius, Rod. |
| 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. |
| Reefer
Slang for insulated van body equipped with refrigeration for controlling temperatures. |
| Reflectors
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 Also: 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. |
| Riser
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 Ibs. of rolling resistance per thousand pounds of gross weight; gravel, 25 Ibs.; and sand, 75 Ibs. This is a vital factor in determining power and power train requirements. |
| Roadside
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 which 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. |
| S - Back to Top |
| SAE
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. |
| Semitrailer
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. which 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 Also: 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 inches on regular models and 48 inches 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 entire load. |
| Side Rails
Upper or lower extensions of the body sides which 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. |
| SM
Abbreviation for "Section Modulus." A measure of frame strength and rigidity determined by the shape, thickness, flange-width and depth of the siderails and reinforcements (if used). |
| Snatch Block
A single or multiple pulley used to reduce cable load or change cable direction. |
| Spacer
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. |
| Spade
One or more hydraulically operated ground-penetrating feet designed primarily to resist rearward movement. |
| Speedability
The speed a vehicle will attain based on engine power, gross weight, power train efficiency, air resistance, grade resistance, and road type. |
| Splash Guard
Deflecting shield at rear of wheels, required by regulation. Also called Mud Flap. |
| Spring Capacity
(a) Capacity at Pad: The total weight that the spring can support in its maximum position; (b) 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. |
| Stabilizers
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. |
| 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. |
| 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. |
| Stroke
(a) In engines, the distance traveled by a piston from top dead center to bottom dead center; (b) 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. |
| 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. |
| T - Back to Top |
| Tachometer
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 Also: Tandem Axle |
| Tail Plate
Rearmost part of the towing or recovery vehicle body. |
| Tail Plate
Rearmost part of the towing or recovery vehicle body. |
| Tandem Axle
Two axles mounted as a group (three axles placed together 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. |
| Thermal Efficiency
The efficiency of an engine in converting heat energy from combustion of fuel into mechanical work. |
| T-Hook
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. |
| Tongue Weight
The amount of the trailer's weight that presses down on the trailer hitch. |
| Torque
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 pounds-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. |
| Tractor
A truck of comparatively short wheelbase used for pulling a semitrailer. |
| 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. |
| Trailer
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. |
| Transmission
A gear reduction device which 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 which 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 which 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. |
| Tread
(a) 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; (b) 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. |
| Truck
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 semitrailer and not so constructed as to carry a load other than a part of the weight of the semitrailer. See Also: Tractor |
| Trunnion
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. |
| U - Back to Top |
| Underlift
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 or occupants. |
| 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. |
| V - Back to Top |
| VCG
Abbreviation for Vertical Center of Gravity, the point at which half of the gross weight is above and half is below. See Also: Center of Gravity |
| Vehicle Equipment Safety Commission
The Commission established pursuant to the joint resolution of the 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 the vehicle for identification purposes, as required by 49 CFR 565. |
| Vehicle Maximum Load on the Tire
That load on an individual tire that is determined by distribution to each axle its share of the maximum loaded vehicle weight 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." |
| W - Back to Top |
| 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). |
| Weight-Sprung
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 Also: Chassis Dimensions |
| Wheelhousing
Housing over wheels replacing floor area to obtain lower floor loading height or lower mounting height. |
| Wheelwell
Housings in body floor to allow clearance over tires. |
| Winch
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. |
| Wrecker
Truck equipped with winch or winches and boom(s) used for recovering and towing vehicles. Term may be used also to mean only the equipment not including the truck chassis. |
| Y - Back to Top |
| 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. |
