Folding bicycle

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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.

Contents 1 Performance 2 Size 3 Challenging perceptions 4 Bicycle Torque Couplings 5 External links 6 References

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.

[edit] Performance

Though folding bicycles can perform as well as conventional bikes, the unusual appearance of most folders (see video demonstrating the typical style of folding a bicycle at YouTube) 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 bike (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.)

In order to make a folding bicycle as compact as possible, certain trade-offs are often made:

Folding bicycles often use small diameter wheels. All else being equal, large diameter wheels give a smoother, less bumpy ride than the smaller diameter wheels. Shock absorbers can be incorporated into the design of a bicycle to give a smoother ride. The shock absorber will absorb some of the energy that would otherwise be used to move the bicycle forward in a more rigid bicycle. Smaller diameter wheels also seem to be less stable [2]

Folding bicycles often have a shorter wheelbase, which results in a rougher ride.

Folding bicycles often break 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 seat posts and steerer tubes which are elongated. These steering mechanisms, which, unlike the shorter stem of a regular bike, sit on top of the frame like a mast, cause larger bending stresses where the tubes meet the frame. There have been sporadic claims in online message forums, and at least one recall due the failure of the steering mechanism.

Folding bicycles universally have many more parts, to allow folding and lock the frame when unfolded. This results in a much more complicated design, with more parts that can fail.

[edit] Size

Folding bikes generally come with a wider range of adjustments than conventional bikes for accommodating different riders.

Seatposts and handlebar stems on folders extend as much as four times higher than conventional bikes. For even greater range of adjustment, longer aftermarket posts and stems are available.

While folders may appear to be "small," the distance between center of bottom bracket, top of saddle and handlebars is often identical to that of conventional bikes, the primary factors in determining if a bike "fits" a rider.

You can see this concept illustrated by this diagram—a 20" wheeled KHS F20 folding bike overlaid on a conventional, 700c wheel (27"), non-folding KHS Flite 100.

The rider's seat, hands and feet are in exactly the same position for either type of bike.

[edit] Challenging perceptions

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".

The wide variety of folding bicycles reflects the different methods to allow a bicycle to fold. For example, bicycles such as the Bazooka simply fold in half. Bikes such as the Birdy and Brompton fold in a more complicated manner but fold smaller. 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's triangular frame folds to resemble a unicycle. Regardless of how each folds, the result is easier to transport and store than traditional bicycles.

[edit] 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]

[edit] External links

• A to B magazine – The place for those interested in folding bikes specifically and environmentaly friendly A to B transport in general.
• Citizen Bike Folding Bike Club - general resource for questions, safety and maintenance for folding bicycle owners.
• 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 - more proof a 1960 bike can still compete with its modern counterparts.
• 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
• Folding Bicycles
• RideTHISbike - folding bicycle videos, specs, photos and reviews

[edit] References

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