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Trailer
A Trailer is generally an unpowered vehicle pulled by a powered vehicle, because powered trailers are more specifically called potrailers. Commonly, the term trailer refers to such vehicles used for transport of goods and materials.
United States
In the United States, the term is sometimes used interchangeably with travel trailer and mobile home, varieties of trailers & manufactured housing designed for human habitation. Their origins lay in utility trailers built in a similar fashion to horse drawn wagons.
In the United States trailers ranging in size from single-axle dollies to 6-axle, 13 ft high, 53 ft long semi-trailers are commonplace. The latter, when towed as part of a tractor-trailer or "18-wheeler", carries a large percentage of the freight that travels over land in North America.
Types of Trailers
Enclosed toy trailers and motorcycle trailers can be towed by commonly accessible pickup truck or van, which generally require no special permit beyond a regular driver's license. Specialized trailers like open-air motorcycle trailers, bicycle trailers are much smaller, accessible to small automobiles, as are some simple trailers, pulled by a drawbar and riding on a single set of axles.
Other trailers, such as utility trailers and travel trailers or campers come in single and multiple axle varieties, to allow for varying sizes of tow vehicles.
Travel trailers
Popup campers are lightweight, aerodynamic trailers that can be towed by a small car, such as the BMW Air Camper and the Coleman Bayside. They are built to be shorter than the tow vehicle, minimizing drag.
Others range from two-axle campers that can be pulled by most mid-sized pickups to trailers that are as long as the host country's law allows for drivers without special permits. Larger campers tend to be fully integrated recreational vehicles, which often are used to tow single-axle dolly trailers to allow the driver to bring small cars on their travels.
Semi-trailers
A semi-trailer is a trailer without a front axle. A large proportion of its weight is supported either by a road tractor or by a detachable front axle assembly known as a dolly. A semi-trailer is normally equipped with legs which can be lowered to support it when it is uncoupled. A single trailer cannot exceed a length of 53 feet in the United States, however it is possible to link several trailers together.
They vary considerably in design, ranging from open-topped grain haulers to normal-looking but refrigerated 13x53' enclosures.
Motorcycle trailer
A motorcycle trailer may be a trailer designed to haul motorcycles behind an automobile or truck. Such trailers may be open or enclosed or open, ranging in size from trailers capable of carrying several motorcycles or only one. They may be designed specifically to carry motorcycles, with ramps and tie-downs, or may be a utility trailer adapted permanently or occasionally to haul one or more motorcycles.
Another type of motorcycle trailer is a motorless wheeled frame with a hitch system designed for transporting cargo by motorcycle. Motorcycle trailers are often narrow and styled to match the appearance of the motorcycle they are intended to be towed behind. No motorcycle manufacturer recommends that its motorcycles be used to tow a trailer.
Trailer winches
Trailer winches are designed to load (or unload) boats and other cargo to and from a trailer. The are made up of a ratchet mechanism and cable. The handle on the ratchet mechanism is turned to tighten or loosen the tension on the winch cable. There are both manual and motorized trailer winches.
Hitching a trailer
The basic function of a trailer coupler is to secure the trailer to the towing vechicle. The trailer coupler attaches to the trailer ball on the hitch of the towing vechicle. The three most common types of couplers are Straight Couplers, A-Frame Couplers, and Adjustable Couplers. A trailer hitch or tow hitch is needed to draw a trailer with a car, truck or other traction engine.
The basic function of a trailer jack is to lift the trailer to a height that allows the trailer to be hitched or unhitched to and from the towing vehicle. Trailer jacks are also used for leveling the trailer during storage. The most common types of trailer jacks are A-Frame Jacks, Swivel Jacks, and Drop-Leg Jacks.
Alternative propulsion trailers
Some trailers are used to power the front vehicles (car, buses, trucks...).
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