Some trailers are made for personal (or small business) use with practically any powered vehicle having an appropriate hitch, but some trailers are part of large trucks called semi-trailer trucks for transportation of cargo.
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.
There also exist highly specialized trailers, such as genset trailers and their ilk that are also used to power the towing vehicle. Others are custom-built to hold entire kitchens and other specialized equipment used by carnival vendors. There are also trailers for hauling boats.
Travel trailer
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 lower 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-trailer
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, called “landing gear”, which can be lowered to support it when it is uncoupled. A single trailer cannot exceed a length of 53 ft 0 in (16.15 m) on interstate highways (unless a special permit is granted) in the United States, however it is possible to link several trailers together.
They vary considerably in design, ranging from open-topped grain haulers through Tautliners to normal-looking but refrigerated 13 ft 0 in (3.96 m) x 53 ft 0 in (16.15 m) enclosures. Many semi-trailers are part of semi-trailer trucks.
Full-trailer
A full-trailer is the US term for a trailer supported by front and rear axles and pulled by a drawbar. In Europe this is known as an A-Frame drawbar trailer.
Close-coupled trailer
A close-coupled trailer is fitted with a rigid towbar which projects from its front and hooks onto a hook on the tractor. It does not pivot as a drawbar does.
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, 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 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. You can get either two wheeled versions or single wheeled version. The single wheeled versions, such as the Unigo or Pav 40/41, are designed to allow the bike to have all the normal flexibility of a motorcycle, usually using a universal joint to enable the trailer to lean and turn with the motorcycle. No motorcycle manufacturer recommends that its motorcycles be used to tow a trailer because it creates additional safety hazards for motorcyclists.
Powered trailer mover
A powered trailer mover is a powered vehicle made to push and pull trailers that require lifting on one end before maneuvering. Some are also called trailer pushers or powered trailer pullers. The powered mover is capable of pushing and pulling an RV, a camper, an equipment trailer, or a boat.
The trailer mover was designed to prevent the strain usually associated with moving large trailered equipment.
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.
Livestock trailer
There are a number of different styles of trailers used to haul livestock such as cattle and horses. The most common is the stock trailer, a trailer that is enclosed on the bottom, but has openings at approximately the eye level of the animals to allow ventilation. The horse trailer is a more elaborate form of stock trailer. Because horses are usually hauled for the purpose of competition or work, where they must be in peak physical condition, horse trailers are designed for the comfort and safety of the animals. They usually have adjustable vents and windows as well as suspension designed to provide a smooth ride and less stress on the animals. In addition, horse trailers have internal partitions that assist the animal in staying upright during travel and protect horses from injuring each other in transit. Larger horse trailers may incorporate additional storage areas for horse tack and may even include elaborate living quarters with sleeping areas, bathroom and cooking facilities, and other comforts.
Both stock trailers and horse trailers range in size from small units capable of holding one to three animals, able to be pulled by a pickup truck or even an SUV; to large semi-trailers that can haul a significant number of animals.
http://en.wikipedia.org/wiki/Trailer_%28vehicle%29