A gravity racer or soapbox is a motorless vehicle which is raced on a downhill road either against the clock or against another competitor. The vehicles are propelled by gravity.
Soapbox cars
Originally, gravity racer cars were built from wooden soap (or apple) crates and rollerskate wheels, but have grown more sophisticated over time, with materials like aluminium, fiberglass and even CFRP being used.
In the United Kingdom a gravity racer car has been called a buggy, trolley, cart. It is currently popularly called a soapbox. In Scotland and northern England it has also been called a bogie, cartie/cairtie, guider or piler. In Wales it is often referred to as a gambo. In Australia they are called billy-carts, and in Brazil it is known as rolimã.
In addition to being built by children, there are organised competitions and races ("soapbox or billycart derby") that often engage the enthusiasm of adults. However, these are usually entered into in a spirit of fun rather than serious competition. Often they will be fund-raisers for charity. Many, but not all, events impose the following rules:
The car must have no motor
The car must have at least 4 wheels
The car may have to have some type of brakes
The driver must wear a helmet
A push at the top is allowed for speed
Soapbox cars weigh an average of and reach top speeds of . Many cities have permanent tracks where drivers compete for prizes.
Construction
A typical gravity racer cart is usually made of steel, and has 4 wheels, arranged as a fixed rear axle, and a steerable front beam axle - usually with a very simple single central pivot. A seat is arranged at the back, and perhaps the seat area is enclosed, as in the original soap-box design. More sophisticated designs might employ a fully enclosed body. The types of wheels employed vary according to what can be obtained easily - wheels from baby carriages, pushchairs, prams, and discarded bicycles being common. Ready-made wheels are also available from hardware suppliers. Steering is typically actuated using a rope connected to the ends of the steerable beam (which can then double as a useful manual pulling device).
More sophisticated steering methods are sometimes seen. Brakes are also commonly used, and most soap-box cart racing contests require these. Often a simple friction brake operated by a lever which bears on one of the tyres is all that is required under the rules.
Gravity racer carts are unpowered, and are either pushed by willing helpers, or are run down a suitable slope. Races will usually take place downhill and the most efficient and skillfully driven cart will win - gravity applying equally to all.
Gravity racer carts also make great construction projects for children, requiring only an intuitive sense of engineering, and a few basic construction skills. There are also pre-designed kits available, though for many this defeats the purpose of the exercise.
Recently, more advanced gravity racers are beginning to emerge. These, intended for competition in the major soapbox races, are sometimes made of carbon fibre and feature a monocoque design, although most use a more traditional chassis or spaceframe design with bodywork made from materials such as plywood, corrugated plastic or similar. Examples of such soapboxes include the Lotus 119c and the Formula Gravity VXR Nimbus.
In Australia billy carts tend to conform, even in the 21st century, to a more traditional or rudimentary specification often being constructed informally by juveniles from found or inexpensive materials with minimal adult input and used without safety equipment. However even when construction of vehicles is more formally organised, such as for the annual Blacktown and District Cub Scout Billy Cart Derby at Rooty Hill, NSW the vehicle is still constructed to a deliberately relatively unsophisticated design, although safety is a consideration.
In Indonesia, billy carts are also known as 'gokar'. They are raced in different regions as a community social activity. The form of the cart is similar to the Australian one. However, the wheels are often motor cycle wheel bearings.
In Brazil, gravity racers are known as "carrinhos de rolimã." Traditional designs are very minimalistic, with an open board-like body and wheels made up of naked ball bearings (no tyres allowed), usually discarded parts obtained from auto mechanics.
History of gravity racer competitions
The first recorded gravity race took place in 1904 in Oberursel (Taunus) near Frankfurt, Germany. It was inspired by major motor sports events like the Gordon Bennett Cup and the Kaiserpreis race.