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 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 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.
Sometimes categorized as folding bicycles, another group of bikes (also called break-away models) separates into pieces rather than fold.

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 enable the bikes to fold, such as small wheels and a shorter wheelbase may give a more rough, ‘twitchy’ ride. To compensate, folders 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 feature increased weight as well as more substantial or additional frame members.

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 utilize 26″ wheels, e.g. the Montague Corporation.
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 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.[6] 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.