Glossary of Terms

Word/Phrase Meaning
ABS An abbreviation for anti-lock brakes.
ADR Australian Design Rule. A set of regulations governing vehicle design (e.g. ADR 38 cover heavy vehicle breaking systems).
AFTERCOOLER See Intercooler.
AGGREGATE MASS The maximum allowable loaded mass of a particular vehicle or combination comprising the GVM OR GCM (Gross Vehicle Mass or Gross Combination Mass).
AIR SUSPENSION A suspension in which the weight of the vehicle is supported by air bags containing compressed air and the axles are held in position longitudinally and laterally by bushed rods.
AIR TRIP An air activated release catch on a tipper tailgate, which is operated from the cab.
ANGEL GEAR Slang term for coasting down hills in neutral, an illegal and dangerous practice. Also called Mexican Overdrive.
ARTICULATED VEHICLE A vehicle with flexibly connected sections. Usually applied to a Prime Mover and semi-trailer as opposed to a truck and trailer which is called a combination vehicle.
AUTOMATIC TOW COUPLING The most common type of heavy trailer hitch in Australia and Europe. The trigger in the coupling automatically releases the spring loaded towing pin when the trailer drawbar eye touches it. Far easier to couple up than the cheaper American type pintle hook. Commonly referred to as a “Ringfeeder”.
AXLE GROUP A group of axles (or single axle) supporting one section of a vehicle. Axle groups in Australia are required to be load sharing.
A-TRAIN Usually refers to a prime mover and semi-trailer towing a trailer.
BALL COUPLING A type of turntable on which the top section rotates on the bottom through a series of bearings.
B-DOUBLE An articulated vehicle with a second semi-trailer attached to the rear of the first semi-trailer by means of a turntable.
BOBTAIL A prime mover without a semi-trailer attached.
BONNETED VEHICLE A vehicle where the driver sits behind the engine that is covered by a bonnet. Bonneted heavy trucks are aerodynamically superior to cabovers because of their wedge shape. They are usually cheaper and lighter than a cabover with the same powertrain, but not as manoeuvrable.
BOG COG A very low gear which is not used in normal circumstance. Also called a crawler, or stump puller.
BOGIE DRIVE A prime mover or truck with two drive axles at the back, a 6×4 or if twin steer 8×4 vehicle. Bogie drive prime movers are the most common in Australia. The drive is usually transmitted from one axle to the other by means of a short drive shaft called a jack-shaft.
BOLSTER A piece of steel or heavy timber firmly attached to the vehicle (often bolted to the chassis) to support the load and/or prevent it moving.
BULKHEAD A term sometimes applied to the gate at the front of a tray body or flat top trailer that is built heavier than side gates. Also called a Loading Rack.
CAB CHASSIS A truck with only the cab fitted. Does not include load carrying or attaching components (e.g. body or turntable).
CAB GUARD A steel structure fitted behind the cab on a prime mover to stop parts of the load striking the cab. Most common in trucks used in the logging industry.
CABOVER OR CABOVER ENGINE (COE) A truck with the cab mounted directly above the engine and front axle. Allows shorter overall vehicle length for better manoeuvrability and has better all round view for the driver. COE trucks are dominant in Europe because they allow longer trailers within an overall length limit.
CAB TARPAULIN A tarpaulin fitted over the top of a load and about halfway down the gates. Used in conjunction with Side Curtains.
CHASSIS A vehicle frame.
CLUTCH BRAKE A device actuated by the last inch of clutch pedal travel which brakes the spinning gears in the transmission. It is used with non-synchronised gearboxes to pick up first or reverse gears when stationary. It can also be used for shifting while going uphill.
CAOMING The side rail of a tray, usually slightly raised.
COMBINATION VEHICLE A rigid truck (or bus) towing one or more trailers.
CONSTANT MESH TRANSMISSION A transmission in which all gears remain in mesh at all times. Ratio changes are effected by means of dog clutches which lock the required gear to its shaft. The driver shifts the dog clutch between two gears compared with a crash box where he actually shifts the gears. Constant mesh gearboxes are non-synchronised and rely on drive skill in controlling engine revs and good timing to shift properly. Roadrangers are the most common constant mesh boxes in Australia followed by Spicers.
CONTAINER A box for the transporting of goods in bulk. Usually fitted with receptacles for twist locks in each corner and provision on the base for forklift handling. Standard lengths are 20 and 40 feet.
CONVERTER DOLLY A unit designed to convert a semi-trailer to a dog trailer. It includes a turntable, a draw bar and an axle group. A dolly can also be a device for spreading the weight of over dimensional loads over more wheels.
CRUISE CONTROL A device that makes the vehicle maintain a pre-set speed and turns off when the driver touches the brakes or accelerator.
CURTAIN-SIDER A van type body with curtain sides that are held down along the sides by straps attached to the tie rail and pulled tight lengthwise by a ratchet. They are increasingly popular because they can be loaded or unloaded from the sides unlike a normal van and they have faster turnaround times than vans or flat tops which require tarping. Most curtain-siders in Australia are Tautliners.
DECK The load-carrying platform.
DOG BOX See Sleeper Box.
DOG A device used to tension chains when securing loads. Expand on description.
DOG TRAILER A trailer with two axle groups, the front group being steered by the drawerbar coupled to the towing vehicle. On some units the turntable can be locked to simplify reversing.
DOLLY See Converter Dolly.
DOUBLE DE-CLUTCHING, DOUBLE CLUTCHING A shifting technique used on non-synchronised gearboxes. It involves letting the clutch pedal out briefly while the gear stick passes through neutral and helps ensure that the gears are spinning at the same speed when they come together. Also called a double shuffle.
DOUBLE TRAILER COMBINATION A vehicle consisting of a prime mover, semi-trailer and a trailer. A two trailer roadtrain.
DRAWBAR STAND A leg that holds a trailer drawbar at coupling height to make hooking up easier.
DRIVE AXLE The axle, differential and wheels that transmit torque to the road.
DUAL WHEELS A matched pair of wheels attached to each end of an axle.
DUNNAGE Packing material (e.g. Pieces of timber, plywood, mats) placed between the cargo and the truck platform or between items of cargo to level the load and/or increase friction if the load is likely to move during transportation. It is also used to leave a gap between the load and deck or different parts of the load so forklifts can get under to lift.
ELECTRIC RETARDER An electric auxiliary brake that works on the drive-train (also known as a Telmar brake).
ENGINE BRAKE OR MOTOR BRAKE An auxiliary brake fitted to an engine (also known as a Jake break, Dynatard, C-brake or Cummins brake) that uses the valves to increase engine retardation.
EXHAUST BRAKE An auxiliary brake that works on the drive-train by restricting the exhaust gases with a slide or butterfly valve.
GROSS COMBINATION MASS OR GCM The loaded weight of an articulated vehicle or combination vehicle.
GROSS VEHICLE MASS OR GVM The loaded weight of a rigid vehicle.
HAULING UNIT A prime mover or rigid motor vehicle being used to tow a trailer.
ISOLATION SWITCH A device which completely disconnects the battery from the electrical system of the vehicle to prevent any possibility of fire due to short circuit.
JINKER A trailer designed to transport long logs.
KINGPIN A pin on a semi-trailer skid plate that locks into a prime mover’s turntable jaws. Also the pin around which a steerable wheel rotates in the vertical axis.
LANDING GEAR OR LANDING LEGS Retractable legs that support the front of a semi-trailer when not coupled to a prime mover. Usually raised and lowered with a two speed crank.
LIFT-UP LAZY A retractable lazy axle that can lift the wheels clear of the ground when the truck is empty.
LINEHAUL Operating on fixed long distance routes.
LIVE LOAD A load that, because it cannot be completely secured, is able to move about within the load space (e.g. bulk liquids, livestock, hanging meat, pneumatic tyred earthmoving machinery).
Reduces the proportion of braking effort going to the rear axle(s) to compensate for forward weight transfer and light or no load. Helps prevent rear wheel lock-up under braking especially when the vehicle is unladen.
LOCKING TURNTABLE A permanent turntable, which can be locked in, the straight-ahead position enabling a dog trailer to be more easily reversed. Greasy plate and ballrace turntables can also be locked for use with semi-trailers that have no blocks behind the kingpin. See turntable.
MAXI-BRAKE See Spring Brake.
OVERDRIVE A gear ratio in which the engine turns more slowly than the tailshaft (e.g. for an overdrive ratio of 0.8:1 the engine turns 8 times for every 10 turns of the tailshaft). Used properly, an overdrive allows the engine to turn more slowly at cruising speed which reduces engine wear and fuel consumption.
OVER-HEIGHT VEHICLE A vehicle that exceeds the maximum permitted height.
OVER-REVVING Occurs when the engine speed exceeds the maximum limit specified by the manufacturer. Usually caused by descending hills too fast and in the wrong gear. This can cause serious damage to the engine. The rev limit is usually marked on a rev counter by a red line.
PANTECHNICON, PANTECH OR PAN A completely enclosed van body on a rigid vehicle, semi-trailer or trailer (e.g. furniture van).
PIG TRAILER A trailer having one non-steerable axle group near the middle of the length of the load carrying platform.
PIN What locks into the drawbar eye on an automatic tow coupler. Also see Kingpin.
POGO STICK A spring mounted pole behind the cab for holding up trailer brake hoses and electrical connections. Can also be spring loaded bar or pole for cargo restraint with ends that fit into recesses in van side walls.
POINT OF ARTICULATION The axis of rotation of a turntable. The pivot or “bending” point of an articulated vehicle.
POWER TAKEOFF OR PTO A device attached to vehicle’s transmission or flywheel enabling engine power to be used to drive ancillary equipment (e.g. tipper hoist, bulk liquid pump, concrete mixer, garbage compactor and hydraulic hoist).
PRIME MOVER A short wheel base truck used to tow a semi-trailer.
REAR MARKER OR REFLECTOR PLATES Red and yellow plates that must be to the rear of heavy vehicles to make them more visible when they are moving slowly or parked.
REEFER A dry freight container, which is insulated and fitted with a refrigeration unit.
RETARDER See Speed Retarder.
RETRACTABLE AXLE An axle that can be raised when not needed – expand on definition, mention auto load sensing.
RIGID MOTOR VEHICLE A vehicle without a trailer.
RINGFEEDER See Automatic tow coupling.
ROADTRAIN Either a truck hauling two or more trailers, or a prime mover and semi-trailer hauling one or more trailers (note: this is not a B-double which consists of a prime mover and two semi-trailers).
ROPE RAIL OR TIE RAIL Usually made of pipe and fitted under the coaming rail. Used for tying ropes, chains and tarps to secure loads.
RPM Revolutions per minute. Also referred to as revs per minute or revs.
SEMI OR SEMI-TRAILER A semi-trailer has one axle group at the rear and is designed so that the front is supported by the prime mover, which is used to tow it. A full trailer has an axle group at both ends and can support itself.
SERVICE BRAKE The main brake system acting on all road wheels and controlled by a foot pedal.
SIDE CURTAINS A tarpaulin that encloses the side of a load. Usually attached to the gates. Can also be the curtains on the side of a Tautliner type truck or trailer body.
SKELETAL OR SKEL TRAILER A trailer or semi-trailer that has no tray but has attachments fitted to the frame for the carrying of goods (e.g. twist locks for containers or bolsters for logs or timber).
SKID PLATE A thick steel plate fixed to the underside of the front of a semi-trailer and incorporating the kingpin (and often a block to keep the skid plate from turning on the upper part of greasy plate and ballrace turntables). The front of the plate is usually curved upwards to enable the prime mover to slide more easily under the trailer during coupling.
SLEEPER BOX A separate sleeping compartment fitted behind but with an opening into the truck cab. Bonnetted longhaul trucks most commonly have sleeper boxes but the trend is for integrated sleepers which cabover trucks have had for years.
SLEEPER CAB A driving cabin that is fitted with one or two bunks.
SPEED LIMITER A device that limits the top speed of a truck without limiting engine revs or power in the lower gears.
SPEED RETARDER An hydraulic or electric auxiliary brake fitted to the driveline which reduces the load on the service brakes.
SPIDER The cast spoke hub of a wheel upon which the rim is mounted.
SPREADER BAR Connects side gates at the top strengthening them and raising the cap tarp in the center so that water runs off when the load height is lower than that of the gates.
SPRING BRAKE A brake that is mechanically applied by a spring and released by air pressure that compresses the spring. Because the brake automatically applies itself if air pressure is lost, it is “fail safe”. Spring brakes are used for parking and emergency braking on air braked vehicles. Also called a Maxi-brake.
SHIFT BAR OR BUS BAR A rigid bar with an eye at each end used to couple road trains for pushing or pulling when one is bogged. The bar is usually about 8 feet long so it can be carried crossways on the back of the prime mover.
STOCK CRATE A truck or trailer body built for carrying livestock. Some states allow stock crates to be up to 4.6 metres high while other trailer types are limited to 4.3 metres. Some states also allow “volume loading” of stock crates where a trailer is built to a certain size and then is not required to weigh in. The size is computed to offer the right weight. This recognizes that it is often impossible to find weighbridges where stock is loaded.
SUPER SINGLE A wide profile wheel and tyre used on a steer axle or in place of a dual wheel assembly on trailers. Properly engineered super single installations on trailers allow wider spring centers and wheel bases for greater stability which is especially important on naturally unstable vehicles like stock crates or tankers. There are also considerable tare weight advantages with super singles, especially when used with aluminium wheels.
TABLE TOP A truck with a flat bed or tray body.
TACHOGRAPH A trip recorder incorporating a clock, speedometer and often a rev counter that inscribes a record of a journey on a circular paper graph. The first tachograph was put on the market in Germany in 1933 and their use is compulsory on heavy vehicles in Europe. The graph itself has not changed since 1933 but the machine was mechanical and is now electronic.
TAILGATE The opening back of tipper trucks and trailers. It can be pivoted at the top so it opens at the bottom, or be hinged at the side for tipping bulky loads such as scrap metal or large rocks. Some tailgates can be adjusted for top and side pivoting.
TANDEM AXLE GROUP OR BOGIE AXLE GROUP A combination of two axles which are related to each other through a load sharing system, with the center of the axles not less than 1.0 metre apart and not more than 2.0 metres apart.
TARE MASS The mass of a vehicle without its load (i.e. when unloaded, without fuel etc.).
TARP OR TARPAULIN A covering traditionally made of canvas that protects loads from rain or dust. Commonly used on flat tops and trays but losing out to enclosed bodies because it takes too long and is too much work with most loads. It is also dangerous from an OH&S perspective.
TAUTLINER The first is still the most common type of curtain sider in Australia. See curtain sider.
TELESCOPIC HOIST An hydraulic hoist fitted to tippers.
TIPPER A truck or trailer that can discharge its load by tilting the cargo body. Also known as a tip-truck or tip-trailer. The Americans call it a dump truck.
TRI-AXLE GROUP A group of 3 load sharing axles with centres of the front and rear axles not less than 2.0 metres apart and not more than 3.2 metres apart.
TRIPLE TRAILER OR TRIPLES A combination of a prime mover, semi-trailer and two trailers. A three trailer road train. Also called triples.
TUG Slang term for a prime mover, especially one used for local work or as ayard shunter.
TURBOCHARGER OR TURBO A device in which a turbine wheel driven at 60,000 to 90,000 rpm by the exhaust gases drives an impeller to pump air into the cylinders under pressure thus increasing engine power and efficiency.
TURNTABLE A device used for coupling a prime mover to a semi-trailer. The three basic types are greasy plate, ball race and fixed. The top of the greasy plate and ball race types move with the trailer and are located by the kingpin and the trailer block. A fixed turntable requires the trailer skid plate to slide around the kingpin while resting on top of the turntable.
TURNTABLE JAWS The parts of the turntable that lock around the kingpin of the semi-trailer.
TWIN STEER AXLE GROUP A combination of two single tyred axles fitted to the front of a truck or prime mover and connected to the same steering mechanism, with centers of axles not less than 1.0 metre and not more than 2.0 metres apart. (The wheels of both axles turn when the steering wheel is turned).
TWIST LOCK A device welded to the frame of a rigid truck or a trailer and used to secure a freight container to the vehicle. One twist lock is used on each corner of the container.
VACUUM SERVO BRAKE A braking system in which the engine vacuum provides power assistance, reducing driver effort in applying the brakes.
WET TANK The tank that receives air direct from the compressor. Most condensation occurs there and the wet tank should be drained as often as possible to protect the air system. Most commonly fitted with automatic drain systems.