Folding bicycles

A folding bicycle is a bicycle designed to fold into a compact form, facilitating transport and storage. When folded, the bikes can be more easily carried into buildings, on public transportation (facilitating mixed-mode commuting and bicycle commuting), and more easily stored in compact living quarters or aboard a car, boat or plane.

Folding mechanisms vary, with each offering a distinct combination of folding speed, folding ease, compactness, ride, weight, durability, and price. Distinguished by the complexities of their folding mechanism, more demanding structural requirements, greater number of parts, and more specialized market appeal, folding bikes may be more expensive than comparable non-folding models. The choice of model, apart from cost considerations, is a matter of resolving the various practical requirements: a quick easy fold, a compact folded size, or a faster but less compact model.

There are also bicycles that provide similar advantages by separating into pieces rather than folding.

Military interest in bicycles arose in the 1890s, and the French army and others deployed folding bikes for bicycle infantry use. In 1900, Mikael Pedersen developed for the British army a folding version of his Pedersen bicycle that weighed 15 pounds and had 24 inch wheels. It included a rifle rack and was used in the Second Boer War.

In 1941, during the Second World War, the British War Office called for a machine that weighed less than 23 lb (this was not achieved - the final weight was about 32 pounds) and would withstand being dropped by parachute. In response, the Birmingham Small Arms Company (BSA) developed a folding bicycle small enough to be taken in small gliders or on parachute jumps from aircraft.

This British WWII Airborne BSA folding bicycle was rigged so that, when parachuted, the handlebars and seat were the first parts to hit the ground (as bent wheels would disable the bike). BSA abandoned the traditional diamond bicycle design as too weak for the shock and instead made an elliptical frame of twin parallel tubes, one forming the top tube and seat stays, and the other the chainstay and down tube. The hinges were in front of the bottom bracket and in the corresponding position in front of the saddle, fastened by wing nuts. The peg pedals could be pushed in to avoid snagging and further reduce the space occupied during transit.

...
Wikipedia