Folding bicycle

A Brompton folding bicycle

Folded Brompton, side view

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 and workplaces or onto public transportation (facilitating mixed-mode commuting) or 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.

Variations include bikes that separate into pieces rather than fold (also called break-away models), as well as recumbent and tandems.

History

Italian Bersaglieri during World War I with folding bicycles strapped to their backs. 1917.

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 a folding version of his Pedersen bicycle for the British army that weighed 15 pounds and had 24 inch wheels. It included a rifle rack and was used in the Second Boer War.

The British WWII Airborne BSA folding bicycle was used from 1939-1945 in the Second World War by British paratroopers. A folding bicycle was developed as a small size was needed to enable it to be taken on parachute jumps from aircraft. The War Office in 1941 called for a machine that weighed less than 23lb and which would withstand being dropped without protection by parachute. BSA abandoned the traditional diamond design as too weak for the shockn and made an elliptical frame of twin parallel tubes, one forming the top tube and seat stays and the other for 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 pedals could be reversed to avoid snagging. The frame weighed 4¾lb.

The bicycle was used by British paratroopers at the D-Day landings and at the Battle of Arnhem.

Shaft-driven folding bike

Performance

Intended for commuter and utility purposes, folding bikes emphasize ruggedness, comfort and convenience, though there are high-end models that emphasize speed.

Design constraints that allow a small folded package, such as small wheels and a shorter wheelbase may give a more rough, 'twitchy' ride. To compensate, folders often feature wider tires and may offer front or rear suspension.

Folding bicycles present challenging structural compromises. They often fold near the frame mid-point (which may weaken or flex) or have elongated seatposts and stems which may experience greater bending stresses. To compensate, folders may weigh more and have more substantial or additional frame members.

Size

Overlaid photos of two KHS bicycles, one a F20 20" wheel folding bicycle and the other a Flite 100 700c wheel racing bike, showing similarities in the geometry and riding position

Folding bikes generally come with a wider range of adjustments than conventional bikes for accommodating different riders, because the frames are usually only made in one size. Seatposts and handlebar stems on folders extend as much as four times higher than conventional bikes. For even greater range of adjustment, longer after-market posts and stems are available. While folding bicycles are usually smaller in overall size than conventional bicycles, the distances between center of bottom bracket, the top of the saddle and the handlebars, the primary factors in determining whether a bicycle fits its rider, are usually similar to that 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 26" wheels, e.g. the Montague Corporation and Dahon.

The A-bike is similar to the Strida but has tiny wheels and compacts a bit smaller. Bikes smaller than a Brompton are often called portable bicycles. They forgo the performance and easy ride benefits of their larger counterparts, acquiring characteristics similar to those of an adult folding kick scooter. Regardless of how each folds, the result is easier to transport and store than a traditional bicycle.

Folding methods

1960s European folding bicycle, showing hinged frame, height adjustable seat post, and quick release handlebar stem allowing the bars to turn parallel to the frame when folded

Folding mechanisms are highly variable.

Half or mid fold Many folding frames follow classic frame pattern of the safety bicycle's diamond frame, but feature a hinge point (with single or double hinges) allowing the bicycle to fold approximately in half. Quick-connect clamps enable raising or lowering steering and seat columns. A similar swing hinge may be combined with a folding steering column. Fold designs may use larger wheels, even the same size as in non-folders, for users prioritizing ride over fold compactness.

Triangle hinge A hinge in the frame may allow the rear triangle and wheel to be folded down and flipped forward, under the main frame tube, as in the Swift Folder and Bike Friday. Such a flip hinge may be combined with a folding front fork as in the Birdy. Swing and flip hinges may be combined on the same frame, as in Brompton and Dahon, which use a folding steering column. Folding mechanisms typically involve latches and quick releases, which affect the speed of the fold/unfold. Bike Friday offers a model, the Tikit, featuring a cable-activated folding mechanism requiring no quick releases or latches, for increased folding speed.

Break away and other styles Bikes may partly fold and partly disassemble for packing into a standard or custom sized suitcase for air travel (e.g., Airnimal and Bike Friday). Other variations include the bicycle torque coupling is a proprietary connector system that can be retrofitted to a standard frame. The Giatex folds and retracts, adjusting to the size of the rider. The Gekko folds from the seat tube like an upside down umbrella. The iXi literally breaks into 2 halves. The Strida has a triangular frame and folds to resemble a unicycle.

Folding mechanisms may incur more cost and weight, allow folding smaller, and tend to use smaller wheels. 24 inch wheels are the largest for which flip hinges are generally used, but smaller wheels, typically 16 or 20 inches, 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, 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.

Usage

Thousands of folding bikes were given to Ikea employees as a Christmas bonus in 2006.

Detail of a Brompton folding pedal

Folding bicycles are particularly suitable for urban commuters. Mixed-mode commuters who deploy the fold mechanism several times daily for portage aboard public transport may prioritize a bike with an easy, quick fold. Marine users, seeking a bike for incidental shore mobility, may prioritize the compactness of the folded bike. Riders using their bikes less frequently may prioritize speed and comfort of ride over ease and quickness of folding. People who live in a small apartment often prefer a folder as it can be more conveniently stored indoors than a full-sized bicycle.

Portability

As folded bikes require less space, they are allowed by some public transportation systems, e.g., Transport for London, which allows folding bikes to be carried at any time on buses and Underground lines. Other public transportation systems may ban or restrict other bicycles, or may require that folding bicycles be enclosed in bags or covers to protect other passengers. Some may restrict folding bikes to off rush-hour periods. Covers range from custom made bags, to bin-liners and shopping bags for smaller folders. Airline baggage regulations may permit folding bikes as ordinary luggage, without extra cost.

Examples

Notable folding bicycles include:

• A-bike
• Bike Friday
• Birdy
• Bridgestone Picnica
• Brompton Bicycle
• Dahon
• Melon Bicycles
• Montague Bikes
• Raleigh Twenty
• Schwinn
• Strida
• Swift Folder
• Tikit

See also

• List of bicycle manufacturing companies
• Portable bicycle - a folding bicycle that is small and light enough to be easily carried afoot or in a cramped vehicle. Portable bicycles compromise riding capability for portability. The technology of portable bicycles constantly evolves, as new concepts and materials are proposed every few years.
• Small wheel bicycle

Further reading

• Hadland, Tony. It's in the Bag!. ISBN 0950743186. 

External links

• Folding bike history
• Travel with Bikes - Folding Bicycles
• Gerson, Jen (22 October 2005). "Know when to fold 'em". Toronto: Globe and Mail. http://www.theglobeandmail.com/servlet/story/LAC.20051022.BIKE22/TPStory/Travel.