Technical Terms

/Technical Terms

Trailer

ADRs- ADRs refers to the Australian Design Rules. The Australian Design Rules are national standards determined by the Australian Government under section 7 of the Act. The full Act can be read at https://infrastructure.gov.au/roads/vehicle_regulation/bulletin/vsb1/all road trailers and caravans must adhere to this document.

Road trailer – A road trailer means.
A vehicle without motive power designed for attachment to a road motor vehicle; or
A piece of machinery or equipment that is equipped with wheels and designed to be towed behind a road motor vehicle.

Very light trailer (TA) – A single-axle trailer with a GTM not exceeding 0.75 tonne.

light trailer (TB) – A trailer with a GTM not exceeding 3.5 tonnes, other than a trailer of Category TA.
medium trailer (TC) – A trailer with a GTM exceeding 3.5 tonnes but not exceeding 10 tonnes.

Aggregate trailer mass (ATM) – ATM is the total mass of the trailer when carrying the maximum load recommended by the manufacturer. This includes mass imposed onto the towing vehicle when the combination vehicle is resting on a horizontal supporting plane.

Gross trailer mass (GTM) – GTM is the mass transmitted to the ground by the tires of the trailer when coupled to a towing vehicle and carrying the maximum load recommended by the manufacturer or importer, approximately uniformly distributed over the load bearing area.

Tare mass – Tare Mass is the total mass of the trailer when not carrying any load, but when ready for service, unoccupied (if relevant) and with all fluid reservoirs (if fitted) filled to nominal capacity except for fuel, which shall be 10 liters only, and with all standard equipment and any options fitted. This includes any mass imposed onto the drawing vehicle when the combination vehicle is resting on a horizontal supporting plane. (Fluid reservoirs do not include water tanks and waste water tanks fitted to caravans).

Payload – The transported load. Freight, excluding the weight of the trailer or tow vehicle.

VIN – Vehicle Identification Number.

Ball height – Refers to the vertical position of the tow vehicle’s tow ball. The ball height will generally have two positions, 1 unloaded or uncoupled & 2 loaded or coupled to a trailer. When coupled to a trailer it is important the ball height be correct from the tow vehicle to the tow device.

Trailer length (Total length) – Length is the longitudinal distance between the ‘Front End’ and the ‘Rear End’ of a vehicle.

Trailer width (Overall width) – Width is the maximum distance measured across the body including wheel guards, but excluding rear vision mirrors, signaling devices and side-mounted lamps.

Chassis width – Refers to the outside width across the outside main members of the of the sub frame the trailer has been constructed on.

Over slung axle – Refers to the mounting of the spring & axle, with over slung combination the axle has been mounted to the underside of the spring.

Under slung axle – Refers to the mounting of the spring & axle, with over slung combination the axle has been mounted on top of the spring.

Hub

Lazy hub – A hub that is in free wheel with no provision of a brake device.

Disc hub – A hub that integrates with a rotor (disc) that provides for a caliper to be attached for braking.

Hub drum – A hub that integrates with a housing (drum) that provides for a backing plate to be attached for braking.

Integral hub – A hub that has been constructed as a single piece.

Two piece – A hub that is constructed from two pieces, usually a lazy hub that is pressed together with either a rotor or drum via the wheel studs or bolts or a lazy hub with a slip over rotor or drum that secures when wheel nuts are tightened.

Dust cap or Grease cap – Usually a pressed steel dome that secures in to the outer nose/spigot of a hub to prevent the contamination of the bearing grease inside the hub.

Bearing buddy – Usually a pressed steel short tube with an internal system comprising of a spring, plate and grease nipple. Grease is pumped through the grease nipple and held under positive pressure to supply the void in a hub with grease decreasing the possibility of grease contamination from foreign materials.

Outer bearing/cone – The bearing in the outside nose/spigot (faces away from trailer body) of the hub.

Inner bearing/cone – The bearing in the inside nose/spigot (faces toward the trailer body) of the hub.

Outer cup/race – The machined ring that is pressed into the hub to contain the bearing in the outside nose/spigot (faces away from trailer body) of the hub.

Inner cup/race – The machined ring that is pressed into the hub to contain the bearing in inside nose/spigot (faces toward the trailer body) of the hub.

Seal – Pressed into the inside nose/spigot of the hub the seal is used to prevent grease seeping out of the hub as well as preventing the contamination of the grease while allowing the hub to spin on the axle spindle.

Single lip seal – A seal that utilizes a single raised lip on the inner face of the seal.

Double lip seal – A seal that utilizes two raised lips on the inner face of the seal.

Register – A circular diameter on the mounting face of the hub that will locate the rim onto the hub.

Marine seal or two piece seal – A seal that is constructed from two pieces. Commonly a steel wear ring that is pressed into the hub that marries to a rubber seal secured to the shoulder of an axle spindle. These seals are more expensive but provide an improved resistance against water entry.

Hub face – The machined surface on the hub where the rim will be secured to once wheel nuts are installed.

PCD– Pitch circle diameter refers to the measurement of the circle diameter where the wheel studs are located and there equal spacing on that circle.

Bearing journal – The internal machined profiles to accommodate the bearing cups and the distances these diameters are apart.

Brakes

Over ride or Over run brakes – A brake system to actuate the trailer brakes via a system contained in the coupling activated by the momentum of the trailer when the tow vehicle is travelling slower than the trailer.

Backing plate – Usually a pressed steel form that contains components (electrical, hydraulic or mechanical) to apply brakes to a hub drum.

Uni servo – A brake cylinder that has one arm or piston to apply pressure to the brake.

Duo servo – A brake cylinder that has two arms or pistons to apply pressure to the brake.

Park– A feature option on some brake assemblies for the ability to apply brakes while the trailer is stationary and disconnected from tow vehicle. Much like a handbrake on your car.

Electric Brakes – A brake system that operates from a voltage input signal to energize the braking magnet, the magnet is drawn to the hub armature surface. The dragging of the magnet on the surface actuates the lever arm which pivots on its assembly and in turn actuates the primary shoe then equalizes through the trailing shoe. When voltage input is removed the magnet de-energizes, releases from the surface and the retractor springs pull the braking shoes back to released position.

Hydraulic Brakes – A brake system that operates on a positive hydraulic pressure to actuate. With Hydraulic drum brakes, the wheel cylinder receives the hydraulic pressure from the brake line and transfers the pressure to the shoes via push rods or pistons. When pressure input is removed the retractor springs pull the braking shoes back to released position. With hydraulic calipers the caliper piston receives the hydraulic pressure from the brake line and transfers directly onto the inner brake pad, depending on the body type of the caliper the pressure is equalized through the inner shoe pulling the body of the caliper together until both out and inner pads clamp the brake rotor. When pressure is released the piston is drawn back into position by vacuum and the brake pads release the rotor.

Mechanical Brakes – A brake system that actuates brakes through a physical mechanical input, usually a rod or wire connected to an “override” system so that as the override system actuates the movement is transferred mechanically through to the brakes to either a caliper or drum type brake. Both mechanical calipers and drums rely on a return spring to release brakes.

Brake Controller – An electronic device mounted inside the cabin of the tow vehicle to interface between the vehicle and the tow device electric brake system. Typical controller’s job is to create a harmony of level of braking required to compensate for varying loads and actuate brakes in emergency situation from the drivers seat.

Breakaway system – A safety system that will work independently to arrest a trailer if it accidentally becomes disconnected from tow vehicle.

Breakaway switch – A safety component with in the breakaway system. Breakaway switches are used to active the breakaway system in the event that a trailer becomes accidentally disconnected from the tow vehicle. The breakaway system should arrest the trailer independently through the trailer brakes.

Axle

Axle profile – The nominated material size that an axle is constructed from.

Carrying capacity – The nominated static load the axle can carry.

Axle nut – The nut that threads to the axle to retain the axle washer, commonly they are “castellated” and are held in position with a split pin.

Tip to tip – The nominated distance of a bare axle measured in a straight line across the length of the axle from the very tip of the threaded end to the same point on the opposite tip of the axle.

Face to face – The nominated distance measured in a straight line across the length of the axle, from the wheel mounting surface of a hub to the wheel mounting surface of the opposite hub.

Overlay axle – An axle beam that has stub axles attached directly on top or either end of the axle beam to slightly reduce the ride height of a tow device.

Drop axle – An axle beam that has plates attached to either end to offset the axis of the stub axles. Used to reduce the ride height of a tow device by 64mm or 100mm.

Camber – A construction option where the axle beam is pressed for a positive camber to compensate for the stress of load. When vertical load is applied the axle beam will straighten out and wheels should be in the correct alignment.

Spindle – The Machined tips of the axle to include bearing shoulders and thread. These must be match to bearings and hub journal.

Parallel – The Machined spindle has the same diameter for the inner and outer bearings.

Tapered – The Machined spindle has a larger inner shoulder diameter and a smaller outer shoulder diameter for a larger inner bearing and a smaller outer bearing.

Flange – A flat plate of steel welded directly to the axle beam to make provision for attachment of a baking plate or caliper.

Park– A feature option on braked axles for the ability to apply brakes while the trailer is stationary. Much like a handbrake on your car.

Spring

Eye slipper – The front facing end of the spring is constructed with a rolled eye, the rear facing end of the spring has a flat tongue. These springs work in conjunction with a hanger that allows the flat tongue to slide when spring is under load.

Eye and eye – Both ends of the spring are constructed with a rolled eye, both eyes have the same inner diameter. These springs work in conjunction with shackle plates to allow for spring growth under load.

Eye Rocker– The front facing end of the spring is constructed with a rolled eye, the rear facing end of the spring has an enlarged eye. These springs incorporate a roller bush that can roll inside the rear larger eye of the spring when it is under load.

Load sharing – A suspension system that allows for weight to be distributed through components from axle to axle to equalize load transmitted to axle group.

Spring leaves– The individual plates of steel that make up a spring pack.
Deflection – The vertical distance change in the camber of a spring when load or shock is applied.

Offset – The location of the bolt in relation to the spring eyes is unequal. Used to bring an axle spacing together, usually for wheel diameters like 14”.
On center – The location of the bolt in relation to the spring eyes is equal. Used to bring an axle spacing apart, usually for larger diameter wheels like 16”.

Shackle plate – A suspension component that connects the spring (eye & eye) to the trailer chassis (hanger). The double pivot of this allows for articulation of the spring in action.

Shackle bolt – The bolt that connects the chassis (hanger) to the spring eye.

Greaser bolt – A shackle bolt that has a grease nipple to allow for grease to be pumped through a central void and through an outlet inside the spring bush.

Wrap – The forming of the material around the connecting end of a spring.

Rim

Rim offset – The internal location of the mounting surface that will attach to the axle. Offsets are “Zero” are absolute middle of the rim, “Positive” the amount of distance the mounting surface is past center away from trailer body and “Negative” the amount of distance the mounting surface is past center towards the trailer.

Rim contour – The internal form of a rim.

Front Space – The amount of space from the outer edge of a rim to the mounting surface.

Back Space – The amount of space from the inner edge of a rim to the mounting surface.

Centre Bore – The open diameter in the center of the rim to allow for the nose/spigot of a hub to pass through.