FOLDING BICYCLE

A 'folding bicycle' or 'folder' is a type of bicycle that incorporates a number of hinges or joints, which may be lockable, that permit it to be folded into a more compact size. Typically this works by folding one or more of the bicycle's components, most often the frame.
Folding bicycles are popular in East Asia and the United Kingdom, but are less common in the United States. Their major advantage is that they can be folded up and taken on public transport and into buildings where conventional bicycles cannot. This has advantages to commuters, as the bicyclist does not have to chain the bicycle in the street. It also allows journeys using public transport to be completed in part by bicycle. Folding also makes transporting a bicycle in an automobile easier. Folding bicycles cost more than non-folding bicycles with the same performance-related features.
As an alternative to folding, some bicycle models achieve similar results by being able to be separated into two parts for easy storage and packing. They are usually grouped in the same category as folding bicycles. See the Bicycle Torque Couplings section below for more details.

Contents

Performance

Size

Folding methods

Challenging perceptions

Bicycle Torque Couplings

External links

References

Performance

Most folding bicycles are intended for commuter and utility purposes, hence emphasize ruggedness, comfort and convenience over speed. A few folders are made for speed, and have been ridden to victory over non folding bikes in races. In the interest of compact folding, certain trade-offs are common:

Most folding bicycles use small diameter wheels. All else being equal, smaller diameter wheels give a rougher ride than larger wheels. Folding bicycles often have a shorter wheelbase, which also contributes to a rougher ride. To avoid losing any more comfort, narrow tires are rarer than for non folders. Suspension systems can be incorporated into the design of a bicycle to give a smoother ride. The suspension, however, will also absorb some of the pedaling energy that would otherwise be used to move the bicycle forward in a more rigid bicycle.
Folding bicycles often separate or fold in the middle of the frame, which, depending on the design, can weaken the frame and cause more energy-absorbing flexing.
Folding bicycles often have elongated seatposts and stems. These longer components, which project above the frame like masts, experience larger bending stresses where they meet the frame, compared to the shorter components of regular bikes. There have been sporadic reports of failure in these components in online message forums, and at least one recall due the failure of the steering mechanism.
Folding bicycles necessarily have more parts, to allow folding and to lock the frame when unfolded. This results in a more complicated design, with more parts that can fail.

Size

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 bicyles, 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.

Overlaid photographs of a 20" wheeled KHS F20 folding bicycle and a conventional, 700c wheel (27"), non-folding KHS Flite 100. The saddle, handlebars and bottom bracket are in more or less the same relative positions on both, and the wheelbase is similar.

Folding methods

The wide variety of folding bicycles reflects the different methods to allow a bicycle to fold. The simplest folding frames have one hinge, for example bicycles such as the Bazooka and Tunturi Chip which simply fold in half. Bicycles built on this pattern usually also have quick-connect clamps to allow raising and lowering the steering and seat columns quickly. A similar swing hinge may be combined with a folding steering column, as in Dahon or Giant Halfway. Simple fold methods tend to use larger wheels, sometimes the same size as in non folders, for users for whom maximum compactness is less important than the virtues of taller wheels. These larger folders are compact enough for a car trunk or boot, though usually too unwieldy to carry onto a bus. Most follow, at least approximately, the classic pattern of the diamond frame safety bicycle. These types were commonly made as a sideline by regular bike manufacturers in the middle 20th century, and late in the century they were refined.
A hinge in the frame may instead be used to 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. 24 inch wheels are the largest for which flip hinges are generally used, but smaller wheels are more common.
Swing and flip hinges may be combined on the same frame, as in Brompton, which also uses a folding steering column. These complexities require more money and weight, allow folding smaller, and tend to use smaller wheels. They also tend to be unique and exclusive; that is one manufacturer uses similar designs on all models, while the products of each manufacturer fold differently from other manufacturers. Smaller size does not mean lighter weight, as most of these designs forego the bracing benefits of the diamond frame, and must compensate as a step-through frame does, with thicker metal.
Bikes such as those from Airnimal and Bike Friday partly fold and partly disassemble. 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. The A-bike is similar to the Strida but has a smaller wheel base and compacts a bit smaller. Bikes smaller than a Brompton are often called portable bicycles. They forego the performance and easy ride benefits of their larger sisters, acquiring merits 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.

Challenging perceptions

Bicycles are not only used for utility purposes; some are for fun. Not having to endure many hundreds of fold/unfold cycles per year or carry them in tight quarters, their buyers are more often willing to compromise foldability to get performance (in the sense of speed) than vice versa. Thus, in places where commuting is rare except by automobile, as in the majority of the United States, folders tend to be larger, faster, simpler, and better adapted to car culture than in places where folders are for transport.
Though folding bicycles can perform as well as conventional bikes, the unusual appearance of most folders () as well as perceptions regarding compromised fit and performance have limited their acceptance.
On the street, folding bikes are capable of high performance. The idea that a folder is slower than a conventional bike does not necessarily hold true.

A Moulton Bicycle (whose frame separates in two) was used to win a criterium race on the streets of Toronto, Canada, where acceleration and maneuverability gave it an edge over conventional bikes. A Moulton was also used to set a human-powered vehicle speed record on an indoor track, behind a pace vehicle. An Airnimal folder was ridden to a 3rd place victory at the world time trial championships.
According to the Bike Friday FAQ, here: [1]
:''"...tests have shown that up to 16 mph the small wheel is more efficient than a big wheel. Between 16 and 33 mph there is little difference. Over 33 mph the gyroscopic effect of the big wheel makes it more effective. Most folks do not go over 33 mph..."'' ''(Note: the Tour de France averages somewhere around 25 mph, and those are world class athletes including the likes of Lance Armstrong.)''
While it's important to shop carefully for a bicycle—including a folder—with an adjustment range to suit the rider and with a suitable drivetrain and tires capable of low-friction and high speed, it's hoped continued education of the consumer will help to popularize the folder by dispelling the myths of "too small, too slow".

Bicycle Torque Couplings

As an alternative to folding, some bicycle models achieve similar results without some of the disadvantages by being able to be separated into two or more parts for easy storage and packing. One commercially available component to facilitate this is the 'Bicycle Torque Coupling' (BTC™) from S and S Machine. They make it possible "to purchase professional quality, full size folding travel bikes, including tandems, from over 100 independent bicycle framebuilders." These manufacturers include Calfee, Co-Motion, Merlin, Santana, Serotta, and Seven^[1]

External links

★ A to B magazine – The place for those interested in folding bikes specifically and environmentally friendly A to B transport in general.

★ AtoZ list by Chop - AtoZ of folding bikes

★ Amtrak passenger trains treat folders as carry-on baggage

★ Bike forums Folding Bike Section - The most popular online folding bike forum.

★ TIME Magazine: Know When to Fold 'Em

★ Sheldon Brown's Raleigh Twenty - The original Hot-Rodded folding bike.

★ Cheg's 'Super-Modified' Raleigh Twenty folder - detailed photographs of '60s folding bike.

★ LittlePixel's Modified Raleigh Twenty site with build photos and a directory of other converted bikes.

★ Folding Bicycle Information compiled by Steven M. Scharf (nordicgroup.us)

★ The Folding Society – guides to choosing a folder and reviews of many types

★ Travel with Bikes - Folding Bicycles

★ RideTHISbike - folding bicycle videos, specs, photos and reviews

★ All About Folding Bikes! - Site dedicated to the Folding Bike.

References

1. S and S Machine Bicycle Torque Couplings


Hadland, Tony. It's in the Bag! – a History in Outline of Portable Cycles in the UK. ISBN 0-9507431-8-6