Glossary › S

Corner radius

The dimension to EG standards from the king pin of a semi-trailer to the front left or right corner of the bodywork. The international standard dimension is 2040 mm so that there is compatibility with tractor units throughout Europe. This is the coupling radius of a semi-trailer.

Fifth wheel coupling position

The fifth wheel on tractor units should be positioned in front of or over the drive axle so that the load can be evenly distributed on the tractor and it’s axles.

Fifth wheel height

Distance from the ground to the top of a fifth wheel. Varies from around 1m to 1.5m depending on semi-trailer type. Mega-trailers require an extremely low fifth wheel in order to maximise internal load height in the bodywork. Semi-trailer tractors with very low fifth wheels are known as low-trucks.

Folding handrail

Folding handrails are usually found on waLKWays above tankers.

Fork-lift axle load

In accordance with CSC requirements rail approved swap bodies must be tested with a floor load of 5460 kg/m².


Step at the front of a semi-trailer chassis from neck to low load deck. Often used for high volume bodywork.

Powder goods

Term used to describe all goods that are dust like and can be transported in silos e.g. chalk, gypsum, grain, etc.

Quick swap prime mover

Special vehicles for moving swap bodies without folding away legs. The low chassis can drive under the body and lift it while standing on legs. Kögel prime mover is called the ‘Wiesel’.

Quick swap vehicles

Vehicles which are primarily used internally to be able to mount, transfer and set down demountable bodies as quickly as possible.


Component used to push brake shoes apart.


Leading German manufacturer of shock absorbers.

Saddle holder

Used on the rear flap of a horse trailer.

Saddle store

Found in the front of a well-equipped horse trailer.


Sauer Axle Factory. Leading German axle manufacturer.

SAF Intraax

Weight saving axles from SAF with integrated brackets for fitting of the chassis frame, air bags, brake cylinders, etc.


Improved version of SAF Intraax.

Safety cable

Safety cable used on car trailers with over-running brakes.

Safety coupling

If accidentally uncoupled the coupling automatically applies brakes or cuts oil supply.

Safety test (SP)

From 01.12.1999 the SP test has replaced the intermediate tests (ZU) and special brake tests (BSU). For trailers over 10 tonne overall weight the SP must to be carried out 6 months after every principal test (HU).

Safety wire

Safety device which connects a tipping container to the vehicle chassis and prevents over-tipping of the container.


A cargo control system developed by the German manufacturer Sommer. Cargo control straps can be attached at any position along the length of a special side rave.

Sand blasting

Steel components are usually sand blasted (with steel particles) to clean the material surface prior to painting.

Sanded floor

Used in refrigerated vehicles to provide a non-slip surface where dampness may be found. The sand is applied to a fresh PVC screed.

Sandwich panels

Trailers and semi-trailers bodywork for refrigerated, chilled and dry freight transport may be manufactured from sandwich panels. The panels are available in a range of thickness and comprise a foam internal core with grp, plywood or metal lining on both faces.

Schmitz spur aggregate

Early mechanical steering double axle aggregate for trailers and semi-trailers. Friction operated with maximum turning of 12°.


Leading German mechanical spring manufacturer.


Supply Chain Management. Term used for the entire logistic chain and associated software.

Scrap material semi-trailer

Special 13.6m semi-trailers for transporting scrap with open-topped steel body and rear doors. These vehicles have limited use other than for scrap.

Screw coupling

Used for hydraulic connections between tractor and trailer.

Seal extrusions

These are sealing sections with multiple lips that are used on the doors of refrigerated vehicles.

Sealing ring

Part of an axle hub that seals in the lubricant.

Secondary safety device

Standardised latch used as a safety device to secure swap body legs when travelling.

Self damping

Rubber torsion axles on car trailers are so constructed that swinging of the vehicle is prevented by the self damping properties of the axle.

Self powered

Electro-hydraulic equipment for lifting secondary decks or tail-lifts on trailers. Control is independent of the tractor unit and is usually powered by batteries on the trailer.

Self supporting

A construction where the body and chassis are integrated rather than two individual components as is traditional. Often used for tank trailers and becoming more common for refrigerated semi-trailers.

Self supporting

Bodies which are so constructed that they do not need support from a chassis e.g. refrigerated semi-trailers and the Setra Bus where Setra is an abbreviation of Selbsttragend.


Vehicle bodies e.g. tankers may be constructed to allow discharge unaided. May be achieved by tipping, automatic walking floors or discharge equipment fitted underneath a tanker body via gravity or compressed air.


Trailer, usually for transporting long goods, which uses turntables and the load to passively steer the trailer behind the tractor.


Term used for semi-trailer.


Trailers with one or more axles at the rear and a king-pin at the front for coupling to the fifth wheel of a tractor unit. Overall allowable length of a semi-trailer road train is 16.5 m.


Universal term for trailers with one or more axles at the rear and a king-pin at the front for coupling to the fifth wheel of a tractor unit. Overall allowable length of a semi-trailer road train is 16.5 m.


Lowering system used on light ball coupled trailers up to 3.5 tonnes. A front mounted hydraulic pump allows the trailer to be lowered to ground level for ease of loading or driving on.

Sensor cables

Part of an ABS brake system.


Leading manufacturer of sliding roof systems.


Telematic equipment in semi-trailers from the French manufacturer GT.


Swap bodies that can be lowered to ground level via mechanical or electro-mechanical equipment in the corner posts.

Shoring pole

Cargo control pole that can be fitted across a body in tracks fitted on the side walls.

Shoring poles

Poles used for cargo control in vehicle bodies.


A full width shute at the rear of tippers that ensures the load is discharged an acceptable distance away from the rear of the vehicle.

Side curtain

Curtainsider curtains are usually tensioned horizontally using ratchets at front and/or rear and vertically using buckles on the bottom of the curtain which hook under the side rave.

Side guards

Safety rails mounted longitudinally between wheels to prevent access under the vehicle.

Side loader

Side mounted lift from the manufacturer Zikun. Most commonly used for beverage vehicles.

Side marker lights

Required on vehicles over 6m in length.

Side post trailer/semi-trailer

Usually used for transporting timber. Removable posts are fitted along the front, rear and sides of the trailer.

Side posts

The roof support posts on the side of a vehicle. May be fixed, removable, sliding, split or swinging.

Side posts

Side posts are usually allowed to slide along the top of the body to allow side loading of long goods.

Side underrun guards

Compulsory equipment fitted to the side of vehicle chassis to prevent other traffic getting under the chassis.

Side wall rails

Cargo control rails on the top of car trailer walls.

Side wall reinforcement

Required in side walls of refrigerated vehicle for hanging meat transport.

Silent bushes

Low wearing bushes used in all types of moving components e.g. bearing eyes of trailer suspension.

Silo container

Tank or silo containers in 20, 30 or 40 foot frame that can be handled as a standard shipping container.

Silo vehicle

General term for tanker or container vehicles that transport powder goods rather than liquids.

Single joint trailer

Term used by the German manufacturer Ackerman-Fruehauf for a tandem trailer type EZ. Operates like a semi-trailer but is coupled under the truck body.

Single leaf side door

Usually found on dry freight bodies where side access is required.

Single leaf suspension

Usually used for lightweight vehicles comprising a single steel leaf as opposed to the usual multiple leaf suspension springs. Offer a weight advantage and more comfortable ride.

Single lever locking

Safety equipment for height control of a draw bar on roll container and skip trailers – easily operated by one person.

Single line brakes

Early brake system in which air pressure is built up in the trailer air lines.

Single line system

On hydraulic tipping trailers a single line is used to fill and discharge the oil – previously one line was required for each.

Single tyres

One axle with only 2 wheels.

Skeletal semi-trailer

Semi-trailer chassis which is used to transport one or more standard ISO containers.


Demountable containers usually steel which are used to collect and transport bulk and waste materials as swap bodies.

Skip tipper

Vehicle used to set down and pick up skip containers. It is an interchangeable system.

Sled chassis

Container semi-trailers with runners above the main beams on which containers can be pushed into position.

Sledge trailer

Trailer for waste disposal containers. The containers are loaded onto the trailer chassis from the rear in a sledge. System has weight advantages over roller operated systems.

Sliding bow body

A body system from the German manufacturer Edscha. The complete body including rear doors can be moved to the front of the vehicle. The trailer can then be loaded as a flat.

Sliding doors

Dry freight bodywork may have sliding doors to allow loading/unloading from the side.

Sliding roof

Sliding roof system that folds together when opened. Leading product types are Edscha and Sesam.

Sliding roof

Roof cover system which slides from front to rear or from rear to front allowing body to be loaded over entire length from above – see Edscha and Sesam.

Sliding side door body

Vehicle body with two or more sliding doors as side walls allowing fast side access.

Sloped ramp

The sloping surface running into the low bed area of a step frame trailer.

SMB axles

French manufacturer of trailer axles.

SN axles

BPW trade name for S cam braked axles.


Semi-trailers for hazardous goods with suction and pressure containers made from V4A material which are used up to 3 bar.


Leading manufacturer of tail-lifts.

Spacing washers

Used to eliminate play in suspension springs and draw bars.

Spare wheel

Additional wheel carried in case of emergency.

Spare wheel basket

Hinged basket used to carry spare wheel. First developed in Sweden.

Special approval

Special approval is required for vehicles that have weights and dimensions outwith standard allowable limits.

Spindle brake

General term for hand operated parking brakes on trailers.

Spindle clamp

A spindle clamp may be used to lock demountable bodies and skips.

Spindle tipping equipment

Light trailers may be tipped to the rear using a spindle system that makes loading easier e. g. a car transporter.

Spiral brake line

Air connection hose between tractor unit and trailer.

Split level loading

This can be done in trailers or semi-trailers with secondary decks that may be fixed or height variable using hydraulic or electric means.


Safety system for air bags – manufacturer Weweler. The system prevents air bags being pulled apart when the trailer is lifted by crane e.g. intermodal trailers being loaded onto rail wagons.


Aerodynamic equipment fitted on top of a vehicle cab or on a body bulkhead.

Sprayed lining

Linings may be sprayed on the internal surface of tankers to protect the tank against aggressive goods.

Spring bracket

Steel supports used to fix front of springs using a bolt.

Spring bushes

Bushes for suspension spring bolts. These bushes are found in the front spring support and can be replaced when worn.

Spring controlled parking brake

Alternative to a hand brake. A spring is operated by air pressure. In the brake cylinder the spring load is applied to the wheel brake. Can only be released using air pressure.

Spring leaf

Individual spring leaf.

Spring lifter

Springs used to help open and close ramps by hand e.g. on low loaders.

Spring operated brake cylinder

Brake cylinder with integrated spring operation. The spring system replaces a traditional hand brake.

Spring pins

Small spring steel safety pins used to secure bolts etc.

Spring supports

Springs used on heavy side and rear drop-sides to assist one man operation.

Spring suspension

There are different types of trailer and semi-trailer suspension i.e. multiple leaf springs, parabolic springs (one to three leafs) and air suspension. Rubber suspension for light axles. Hydraulic suspension for heavy axles.

Spruce flooring

Spruce is used for vehicle floors that must carry high loads e.g. low loaders and heavy material transporters.


Longitudinal torsion tube which, via a wedge coupling and the tipping hydraulics, stiffens the frame so that the vehicle cannot fall over when tipping. Patented by the company Fahrzeugfabrik Hoffmann.


Empty steel swap bodies may be made stackable like ISO containers to save space. Fitted with fork-lift pockets.

Stainless steel

Used for manufacturing tank vehicles and increasingly for dry freight bodywork especially because of extended vehicle life, strength, anti-corrosion and aesthetics.

Steel body

Reinforced steel trailer bodies are generally used for bulk goods like scrap, rubble and stone.

Steel chassis

Chassis for trailers and semi-trailers are almost always constructed in steel. Fine grain steel with higher strength and lower weights are increasingly used. Aluminium chassis are built where extremely low tare weight is required.

Steel drop-sides

Used on low cost tilt bodies – cheaper than aluminium. Double skin reinforced steel drop-sides are better suited to heavy-duty tippers.

Steel trough

Steel troughs are used for bulk building materials or rubble. Usually tip to the rear and are easily recognised by large external reinforcing profiles.


Various steering systems are available for trailers and semi-trailers. These can be operated by hydraulic, rod, hydrostatic or other systems.

Steering axle

Trailer axles that can be steered by cables, hydraulics or friction. Often required to give a trailer better turning characteristics e.g. to meet standard turning circle requirements.

Steering brace

Component of a steering system (Schmitz Cargobull).

Stop cable

Component used with skips.


Measured in kilograms per square millimeter (kg/mm²). An important material characteristic used in bodybuilding.

Stub axle

Single wheel with brake drum and hub on a short piece of axle. These are used on special vehicles that cannot have a complete axle running across the vehicle e.g. where the internal loading area needs to be uninterrupted.

Stub axle suspension

Suspension on single wheel hubs. Often used for special vehicles without flooring whereby the entire volume in the body (even down to the ground) is available for loading. Also used on car trailers where the suspension is via a special rubber torsion stub.

Stub axles

These are single wheel hubs with individual suspension. Often used for special vehicles without flooring whereby the entire volume in the body (even down to the ground) is available for loading. Also used on car trailers where the suspension is via a special rubber torsion stub.

Super pallet width

Old term for vehicles with internal width of 2460mm when maximum external width was only 2500mm.

Support for landing legs

Angle support under a swap body that holds landing legs when not used.

Support width

Distance between the support legs of cranes.

Suspension bolts

The vertical bolts which clamp the springs together and fixes them to the axle.

Suspension bolts

The vertical bolts which clamp the springs together and fix them to the axle.

Suspension brackets

Bracket used for fixing the front of suspension springs to chassis using bolts. Carries suspension load.

Suspension centres

The distance between the centre of suspension springs – often the same distance between V-drawbar blocks.

Suspension diagram

Load and performance diagram for loaded and unloaded leaf springs.

Suspension guide

Guide which allows the rear end of a suspension spring to slide backwards when under load.

Suspension hangers

Hangers between springs and chassis brackets.

Suspension plates

Plates which are fixed to axle body and used to support suspension springs.


German air conditioning and refrigeration unit manufacturer.

Swap trailer

Invention of a German manufacturer in order to produce a semi-trailer with internal load deck of 15.3m which used dimensional regulations to the limit, like a draw-bar trailer combination.These vehicles are not built by Schmitz Cargobull any more.

Swap trailer

Invention of a German manufacturer for a semi-trailer with internal load deck of 15.6 m which used dimensional regulations to the limit. Never approved or brought onto the market.


Anti-theft device fitted to the corner castings of containers and swap bodies.

Swing board system

Opening system of a high volume beverage semi-trailers. The side walls were folded down and partly folded up onto the roof.

Swing out area

The area that is covered by the overhang behind a vehicles rear axle which when turning.

Swinging crossmember

Roof crossmember that swings to the side allowing quick access through the roof.

System length

Since 01.09.1997 the maximum length from front edge of the towing vehicle load deck to the rear edge of the trailer load deck may not be greater than 16.4m. This is the overall length of a road train not including driver cab.

Trailing curtain

Continuous unloading or walking floor systems may have internal walls that move with the floor. These walls have a trailing curtain at the bottom to ease discharge and help clean the vehicle.