Dolly

A dolly is a wheeled chassis with one or more axles and equipped with fifth wheel coupling and a drawbar to tow and support the front end of a semi-trailer or convert a semi-trailer into a full trailer.^[1]

Dollies are also designed to move heavy objects or shipments and are used for storage as well as transporting or hauling recreational vehicles, motorcycles, snowmobiles, or garden tractors. A dolly may also be used as a small trailer for towing one vehicle behind another. This type of dolly, also called a tow dolly, is a basic configuration of a two-wheeled platform, an axle, and a tow-hitch.^[2]

[edit] Features/How it Works/Types

The two types of dollies used to support semi-trailers are converter dollies and gooseneck or low loader dollies.

Converter dollies have one, two, or sometimes three axles designed specifically to provide auxiliary axle front-end support to semi-trailers. Semi-trailers only have suspension and wheels located at the rear so a converter dolly must be used to compensate for wheels and suspension at the front end of the semi-trailer near the rear end of the truck tractor. If a semi-trailer is used as a second or third vehicle in a road train, it is converted to a full trailer using a dolly. Converter dollies come equipped with one or two axles and feature fifth wheel coupling, located directly above and forward of the center of suspension, and a single or double-tow-drawbar arrangement. The coupling attached to the semi-trailer is supported and towed by the converter dolly.^[3]

Converter dollies come in two variants. An A-dolly is defined by its single-point tow bar and accounts for 99 percent of the dollies used in the U.S. today. With regard to the towing trailer, a single-point hitch permits the dolly to articulate yaw or steering, pitch (rotation), and rolling. A C-dolly has a double-tow-bar configuration. Originating in Canada, the C-dolly was initially known as a B-dolly. The primary advantage of a C-dolly is its ability to improve stability between multiple-trailer vehicles.^[4] The double-tow-bar of the C-dolly between two trailers works to provide two articulation points as opposed to three, in addition to roll and coupling stiffness.^[5]

Low loader dollies usually have two axles and are also called gooseneck dollies because they come equipped with a gooseneck drawbar that connects to the fifth wheel coupling at the rear of a truck tractor or prime mover. This type of dolly is designed to distribute the weight of the fifth wheel onto the dolly between the truck tractor and the wheels of the dolly.^[6]

[edit] References

1. ↑ Converter Dolly. Top500 Lexicon Database. 2008-11-18.
2. ↑ Dolly Product Description. eBay UK. 2008-11-18.
3. ↑ Converter Dollies. University of Michigan Transportation Research Institute.2008-11-18.
4. ↑ Converter Dollies. University of Michigan Transportation Research Institute. 2008-11-18.
5. ↑ Safety. U.S Department of Transportation. Federal Highway Administration. 2008-11-18.
6. ↑ Dolly Product Description. eBay UK. 2008-11-18.