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, complexity 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.[1]
There are also bicycles that provide similar advantages by separating into pieces rather than folding.[2]
Military interest in bicycles arose in the 1890s, and the French army and others deployed folding bikes for bicycle infantry use.[3] In 1900, Mikael Pedersen developed for the British army a folding version of his Pedersen bicycle that weighed and had wheels. It included a rifle rack and was used in the Second Boer War.[4]
In 1941, during the Second World War, the British War Office called for a machine that weighed less than (this was not achieved - the final weight was about) 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.[5] 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.
From 1942 to 1945, the British WWII Airborne BSA folding bicycle was used by British & Commonwealth airborne troops, Commandos, and some infantry regiments; some were also used as run-abouts on military bases. The bicycle was used by British paratroopers, Commandos, and second-wave infantry units on the D-Day landings and at the Battle of Arnhem.[6]
The 1970s saw increased interest in the folding bike, and the popular Raleigh Twenty and Bickerton Portable have become the iconic folders of their decade. It was, however, the early 1980s that can be said to have marked the birth of the modern, compact folding bicycle, with competing models from Brompton and Dahon.[7] Founded in 1982, by inventor and physicist Dr. David Hon and his brother Henry Hon, Dahon has grown to become the world's largest manufacturer of folding bikes,[8] with a two-thirds marketshare in 2006.[9]
Folding bikes generally come with a wider range of adjustments for accommodating various riders than do conventional bikes, because folding bike frames are usually only made in one size. However, seatposts and handlebar stems on folders extend as much as four times higher than conventional bikes, and still longer after-market posts and stems provide an even greater range of adjustment.
While folders are usually smaller in overall size than conventional bicycles, the distances among the center of bottom bracket, the top of the saddle, and the handlebars - the primary factors in determining whether or not a bicycle fits its rider - are usually similar to those of conventional bikes. The wheelbase of many folding designs is also very similar to that of conventional, non-folding, bicycles.
Some manufacturers are producing folding bikes designed around folding systems that allow them to use wheels, e.g., Dahon, KHS, Montague, and Tern Bicycles. Advantages of smaller wheels include potential for more speed, quicker acceleration, greater maneuverability, and easier storage.[10] For example, the A-bike is similar to the Strida but has tiny wheels and folds a bit smaller. Bikes with smaller than wheels are often called portable bicycles. These forgo the performance and easy ride benefits of their larger counterparts, acquiring characteristics similar to those of an adult folding kick scooter. Nonetheless, regardless of how each bike folds, the result is easier to transport and store than a traditional bicycle.[11]
Folding mechanisms are highly variable.
Folding mechanisms may incur more cost and weight, allow folding smaller, and they tend to use smaller wheels. wheels are the largest for which flip hinges are generally used, but smaller wheels, typically, are more common.
Smaller size does not mean lighter weight, as most of these designs forgo the bracing benefits of the diamond frame and must compensate as a step-through frame does, with thicker metal. The step-through design is a boon to a wider range of rider size, age, and physical ability.
Another system found on folders, such as Montague Bikes, utilizes the seat tube as a pivot point for the frame to fold. This system uses a tube within a tube design to give the bike more torsional stiffness. It allows the user to fold the bike without "breaking" any vital tubes down, thus preserving the structural integrity of the diamond frame. This system is operated by a single quick release found along the top tube of the bike.
The primary purpose of folding a bike is to increase its portability. This is so that it may be more easily transported and stored, and thus allow greater flexibility in getting from A to B.[13] Many public transportation systems ban or restrict unfolded bicycles, but allow folded bikes all or some of the time. For example, Transport for London allows folding bikes at all times on the Underground, but on buses it is down to the driver's discretion.[14] Some transport operators only allow folding bicycles if they are enclosed in a bag or cover. Airline baggage regulations often permit folding bikes as ordinary luggage, without extra cost.[15] Singapore has also implemented new laws to allow folding bicycles in its rail and bus transportation system, with certain size and time limitations.[16]
The first folding electric bike was the Honda Step Compo in 2000. Many more were introduced in the next 20 years.[17]
Notable folding bicycles include: