A Trailer is generally an unpowered vehicle pulled by a powered vehicle. Commonly, the term trailer refers to such vehicles used for transport of goods and materials.
Sometimes recreational vehicles, travel trailers, or mobile homes with limited living facilities where people can camp or stay have been referred to as trailers. In earlier days, many such vehicles were towable trailers.
In the United States, the term is sometimes used interchangeably with travel trailer and mobile home, varieties of trailers and manufactured housing designed for human habitation. Their origins lay in utility trailers built in a similar fashion to horse drawn wagons. A trailer park is an area where mobile homes are placed for habitation.
In the United States trailers ranging in size from single-axle dollies to 6-axle, 13.5 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.
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.
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.
They vary considerably in design, ranging from open-topped grain haulers to normal-looking but refrigerated 13x53' enclosures. Many semi-trailers are part of semi-trailer trucks.
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.
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.
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.
A trailer coupler is used to secure the trailer to the towing vechicle. The trailer coupler attaches to the trailer ball. This forms a ball and socket connection to allow for relative movement between the towing vehicle and trailer while towing over uneven road surfaces. The trailer ball is mounted to the draw bar, which is usually removable. The draw bar is secured to the trailer hitch by inserting it into the hitch receiver and pinning it. The three most common types of couplers are Straight Couplers, A-Frame Couplers, and Adjustable Couplers.
Another type of hitch is known as a "fifth" wheel. Fifth wheel coupling is used with gooseneck style trailers to attach the trailer to the bed of the towing vehicle, ahead of the rear wheels. This type of hitch is used for larger trailers and provides considerably more stability than does a traditional bumper-pull hitch.
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. Some trailers, such as horse trailers, have a built-in jack at the tongue for this purpose.