Trailers can be divided into full trailers and semi-trailers. What is the difference between them? What are their characteristics?
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1. Definetion of trailers, full trailers and semi-trailers
1) Definition of trailers
Trailers means a vehicle towed by a tractor/truck/car without its own power drive. A tractor/truck/car can tow one or more trailers. The truck or tractor is called the master vehicle. The towed section is called a trailer.
The combinations of a tractor/truck/car and a trailer/trailers are the important vehicle transportation type in modern society, which is very effective and simple means to improve economic benefits. It has the advantages of rapidity, mobility, flexibility and safety.
2) Definition of semi-trailers
Semi-trailer is a trailer whose axles are placed behind the center of gravity of the vehicle (when the vehicle is evenly loaded) and is equipped with a coupling device (king pin) that can transmit horizontal and vertical forces to the tractor. Part of the total load of the trailer is borne by the tractor.
3)Definition of full trailers
Full trailer is a kind of trailer which has no power, the vehicle body is equipped with front and rear axles, and can independently bear its own load.
In addition, there is a full trailer with one or two axles at the middle or rear of the vehicle body, and there is a jack to support in the front of vehicle body.
2. There are four main differences between a semi-trailer and a full trailer
1) The connection mode and stress characteristics of the trailer body and the tractor are different
The full trailer is connected with the tractor(heavy towing truck) through a simple hook. The tractor/truck does not need to bear the trailer load, just only provides dynamic tension to help the trailer overcome the road friction resistance. Therefore, the stress characteristic of the connection is mainly the tensile force in the horizontal direction.
The semi-trailer needs a support point provided by the tractor（heavy towing Truck). In addition to providing power, the tractor also needs to bear about half of the load of the semi trailer. Therefore, the force at the coupling(king pin and fifth wheel) of semi-trailer is not only the tensile force in the horizontal direction but also the supporting force in the vertical direction provided by the tractor. Therefore, the special tractor generally has more than two axles.
2) Upright (independent parking) mode is different
The full trailer is generally in a two axles layout. The axles are distributed at the front and rear of its body, so it has the ability to stand upright (park independently) relying on its own tires.
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The axle of semi-trailer is generally composed of multiple axles and concentrated in the rear of the body. It must rely on the front landing gear to achieve its own upright (independent parking) state.
3) Different components
Full Trailer: it is composed of a complete set of chassis, body, towing device, steering device, suspension, walking system, braking system and signal system.
Semi Trailer: compared with full trailer, there is no steering device, but king pin is added; there is no axle in front, but the front support device (landing gear) is added. The front structure is relatively simple, so that the frame floor can be arranged lower and has the advantage of low center of gravity.
4) Different usage scenarios
The full trailer is mainly used for short-distance transportation in farms, factories, families, companies, ports, docks, warehouses and other fields.
Common full trailers are as follows :
boat-trailers, livestock trailers, cargo trailers, RV trailers, travel trailers, utility trailers....
The semi trailers are mainly used for long-distance transportation of goods.
Common semi trailers are as follows:
Tyre
Always check the flatbed semi-trailer tire pressure regularly and check the tire sidewall for cracks and the tread for excessive wear. For wheels, more specifically, regularly check how tight the nuts are.
Brake
Another important item in the checklist is to check the brake lines and pads for cracks or signs of corrosion. Also, make sure the handlebars are well sealed and the brakes respond when the brake pedal is pressed. Flatbed semi-trailer brake failure is a truck driver's worst nightmare.
Lamp
One of the most important items to check is whether the flatbed semi-trailer lights are completely functional. Make sure the brake lights, tail lights, and signal lights are all working properly. Flatbed semi-trailer lights are an extremely dangerous safety hazard, especially when driving early in the morning or late at night.
Electric
Nowadays, many operations on flatbed semi-trailers are carried out by electrical connections. Regardless of whether the system affects the lighting, cooling, or any other function of the flatbed semi-trailer, it is important to double-check that the electrical connection between the towing vehicle and the flatbed semi-trailer is correct. If using a refrigerated flatbed semi-trailer, pre-run, open the door and visually inspect for corrosion.
Fluids and lubrication
Regarding the fluids and lubrication of flatbed semi-trailers, it is important to remember that the fifth wheel must be properly lubricated to avoid excessive wear. When handling engine fluids, check for any leaks underneath the flatbed semi-trailer. One area that requires special attention is the refrigeration compressor of flatbed semi-trailers. A faulty compressor can cause the refrigeration unit to become inoperable, which can damage the product in the flatbed semi-trailer. Confirming that the refrigeration unit is properly charged and cleaning the condenser and evaporator can help ensure that the system is functioning properly.
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