Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Semi Trailer shopping experience:

1. Compare - without doubt the biggest advantage that the Semi Trailer offers shoppers today is the ability to compare thousands of Semi Trailer at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Semi Trailer? Wrong! If the Semi Trailer is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Semi Trailer then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Semi Trailer? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Semi Trailer and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Semi Trailer wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Semi Trailer then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Semi Trailer site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Semi Trailer, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Semi Trailer, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

A semi-trailer is a Trailer (vehicle) without a front axle. A large proportion of its weight is supported either by a Tractor unit or by a detachable front axle assembly known as a dolly (trailer). A semi-trailer is normally equipped with legs which can be lowered to support it when it is uncoupled.

A Tractor unit coupled to a semi-trailer is often called a semi-trailer truck or semi. Though most road trailers meet this definition, the term is most often applied to heavy trailers appropriate for use in such a rig.

Advantages and disadvantages . Advantages In road haulage semi-trailers predominate over Trailer (vehicle)#Full trailers because of their flexibility in use.

• The trailers can be coupled and uncoupled quickly allowing them to be shunted for loading and to be trunked between depots.
• In the event of a breakdown, a tractor unit can be exchanged quickly and the load delivered to its destination without undue delay and without having to trans-ship.
• It is also possible to use a dolly to tow a semi-trailer behind a rigid truck, or behind another semi-trailer.
• Special tractors (known as tugs, yard dogs or yard trucks) are often used for internal transport, for example, manoeuvring semi-trailers at a depot or loading and unloading ferries. These tractors may lift the coupling so that the trailer legs clear the ground.
• Compared with a full trailer, a semi-trailer attached to a tractor unit is easier to reverse, since it has only one turning point (the coupling), whereas a full trailer has two turning points (the coupling and the drawbar attachment).
• Compared with a rigid vehicle, a semi-trailer truck has a turning circle smaller than its overall length making it more maneuverable.

Disadvantages

• Since a semi-trailer rests on top of a tractor it has a high centre of gravity which makes it less stable than a rigid vehicle.
• Articulated vehicles are difficult to drive in snow and ice since they lose traction more easily than a straight truck.
• They are also subject to jackknifing.

Couplings There are two types of couplings: fifth wheel and automatic. In some applications, no separable coupling is fitted and the trailer is bolted to the tractor unit using a bearing and rocker feet as are used under a fifth wheel skid plate.

Fifth wheel coupling The towing vehicle has a wide coupling plate known as a fifth wheel coupling bolted onto its chassis on which the semi-trailer rests and pivots. As the tractor reverses under the trailer, a king-pin under the front of the trailer slides into a slot in the skidplate and the jaws of the fifth wheel close on to it. The driver has to raise the trailer legs manually and couple the airbrake lines and electrical cable. On tractor-trailers that have different colored lines, the red and blue lines are air lines used in brake operations, and the green one is the electrical line.

Automatic couplings Many years ago automatic couplings predominated but are now quite rare. Automatic couplings were generally used for payloads of 12 tons or less, e.g. on the Scammell Lorries.

There is no coupling plate on the tractor. There is a turntable permanently fixed to the underside of the trailer. This locks on to the chassis of the tractor. When the tractor reverses under the trailer its legs rise and the brake and electrical connections are made automatically. Almost the entire coupling and uncoupling procedure is operated by the driver from inside the cab, except that he or she has to descend to release (or apply) the trailer parking brake.

Battery semi-trailer A battery propulsion semi-trailer is a semi-trailer that contains the batteries that are used to power an electric truck or bus.

Types Different types of semi-trailers are designed to haul different cargoes. BoxThe most common type of trailer can haul almost anything that can fit inside. Also called a van trailer.

Curtain siderA curtain sider is similar to a box trailer except that the sides are movable curtains made of renforced fabric coated in with a waterproof coating. The purpose of a curtain sider is to allow the security and weather resistance of a box trailer with the ease of loading of a flatbed.

Reefer (container) - see Refrigerator truckBox trailer with a heating/cooling unit (reefer) attached. Used for hauling produce, ice cream, etc.

Tanker - see Tank truckUsed for hauling liquids like gasoline, milk, etc.

Dry BulkResembles a big tanker, but is used for sugar, flour and other dry powder materials.

FlatbedConsists of just a load floor and removable side rails, and a bulkhead in front to protect the tractor in the event of a load shift. Can haul almost anything that can be stacked on and strapped down.

LowboyType of flatbed in which the load floor is as close to the ground as possible. Most commonly used to haul heavy equipment, cranes, bulldozers, etc.

Car carrying trailerCarries multiple cars; usually new cars from the manufacturer.

Step trailerA step trailer is a trailer on which the floor steps down a level once clear of the tractor unit, the most common types of step trailer are flatbeds and curtain siders.

Double DeckerDouble deckers or deckers are trailers with either a fixed, hinged or moveable second floor to enable them to carry more palletised goods, in general a double decker can carry 40 pallets as opposed to 26 for a standard trailer. Double deck trailers are generaly a stepped box or curtain siders, with box trailers having either a fixed or movable (floating ) deck and curtain sides having either a fixed or hinged second deck, this hinged seconed deck generally swings into a position down the length of the trailer and can be divided into 2 or 3 sections to allow greater load flexibility.

See also

• Air brake (road vehicle)
• Articulated vehicle
• Brake
• Jackknifing
• Semi-trailer truck
• Trailer (vehicle)

External links A semi-trailer is a Trailer (vehicle) without a front axle. A large proportion of its weight is supported either by a Tractor unit or by a detachable front axle assembly known as a dolly (trailer). A semi-trailer is normally equipped with legs which can be lowered to support it when it is uncoupled.

A Tractor unit coupled to a semi-trailer is often called a semi-trailer truck or semi. Though most road trailers meet this definition, the term is most often applied to heavy trailers appropriate for use in such a rig.

Advantages and disadvantages . Advantages In road haulage semi-trailers predominate over Trailer (vehicle)#Full trailers because of their flexibility in use.

• The trailers can be coupled and uncoupled quickly allowing them to be shunted for loading and to be trunked between depots.
• In the event of a breakdown, a tractor unit can be exchanged quickly and the load delivered to its destination without undue delay and without having to trans-ship.
• It is also possible to use a dolly to tow a semi-trailer behind a rigid truck, or behind another semi-trailer.
• Special tractors (known as tugs, yard dogs or yard trucks) are often used for internal transport, for example, manoeuvring semi-trailers at a depot or loading and unloading ferries. These tractors may lift the coupling so that the trailer legs clear the ground.
• Compared with a full trailer, a semi-trailer attached to a tractor unit is easier to reverse, since it has only one turning point (the coupling), whereas a full trailer has two turning points (the coupling and the drawbar attachment).
• Compared with a rigid vehicle, a semi-trailer truck has a turning circle smaller than its overall length making it more maneuverable.

Disadvantages

• Since a semi-trailer rests on top of a tractor it has a high centre of gravity which makes it less stable than a rigid vehicle.
• Articulated vehicles are difficult to drive in snow and ice since they lose traction more easily than a straight truck.
• They are also subject to jackknifing.

Couplings There are two types of couplings: fifth wheel and automatic. In some applications, no separable coupling is fitted and the trailer is bolted to the tractor unit using a bearing and rocker feet as are used under a fifth wheel skid plate.

Fifth wheel coupling The towing vehicle has a wide coupling plate known as a fifth wheel coupling bolted onto its chassis on which the semi-trailer rests and pivots. As the tractor reverses under the trailer, a king-pin under the front of the trailer slides into a slot in the skidplate and the jaws of the fifth wheel close on to it. The driver has to raise the trailer legs manually and couple the airbrake lines and electrical cable. On tractor-trailers that have different colored lines, the red and blue lines are air lines used in brake operations, and the green one is the electrical line.

Automatic couplings Many years ago automatic couplings predominated but are now quite rare. Automatic couplings were generally used for payloads of 12 tons or less, e.g. on the Scammell Lorries.

There is no coupling plate on the tractor. There is a turntable permanently fixed to the underside of the trailer. This locks on to the chassis of the tractor. When the tractor reverses under the trailer its legs rise and the brake and electrical connections are made automatically. Almost the entire coupling and uncoupling procedure is operated by the driver from inside the cab, except that he or she has to descend to release (or apply) the trailer parking brake.

Battery semi-trailer A battery propulsion semi-trailer is a semi-trailer that contains the batteries that are used to power an electric truck or bus.

Types Different types of semi-trailers are designed to haul different cargoes. BoxThe most common type of trailer can haul almost anything that can fit inside. Also called a van trailer.

Curtain siderA curtain sider is similar to a box trailer except that the sides are movable curtains made of renforced fabric coated in with a waterproof coating. The purpose of a curtain sider is to allow the security and weather resistance of a box trailer with the ease of loading of a flatbed.

Reefer (container) - see Refrigerator truckBox trailer with a heating/cooling unit (reefer) attached. Used for hauling produce, ice cream, etc.

Tanker - see Tank truckUsed for hauling liquids like gasoline, milk, etc.

Dry BulkResembles a big tanker, but is used for sugar, flour and other dry powder materials.

FlatbedConsists of just a load floor and removable side rails, and a bulkhead in front to protect the tractor in the event of a load shift. Can haul almost anything that can be stacked on and strapped down.

LowboyType of flatbed in which the load floor is as close to the ground as possible. Most commonly used to haul heavy equipment, cranes, bulldozers, etc.

Car carrying trailerCarries multiple cars; usually new cars from the manufacturer.

Step trailerA step trailer is a trailer on which the floor steps down a level once clear of the tractor unit, the most common types of step trailer are flatbeds and curtain siders.

Double DeckerDouble deckers or deckers are trailers with either a fixed, hinged or moveable second floor to enable them to carry more palletised goods, in general a double decker can carry 40 pallets as opposed to 26 for a standard trailer. Double deck trailers are generaly a stepped box or curtain siders, with box trailers having either a fixed or movable (floating ) deck and curtain sides having either a fixed or hinged second deck, this hinged seconed deck generally swings into a position down the length of the trailer and can be divided into 2 or 3 sections to allow greater load flexibility.

See also

• Air brake (road vehicle)
• Articulated vehicle
• Brake
• Jackknifing
• Semi-trailer truck
• Trailer (vehicle)

External links