Single-speed bicycle

A single-speed bicycle is a type of bicycle with a single gear ratio. These bicycles are without derailleur gears, hub gearing or other methods for varying the gear ratio of the bicycle. Historically, all bicycles were single speed bicycles, specifically fixed-gear or fixed wheel single speed bicycles that had no mechanism to vary the gear ratio or to allow the pedals to coast while the drive wheel moved.

Many individuals looking to improve the efficiency, speed and comfort for bicycle riders developed freewheel systems and gearing systems for bicycles. The term 'single speed' in this article refers to modern bicycles.

There are many types of modern single speed bicycles; BMX bicycles, most bicycles designed for children, cruiser type bicycles, classic commuter bicycles, unicycles, bicycles designed for track racing, fixed gear road bicycles, and fixed gear mountain bicycles.

Most fixed-gear bicycles or fixed wheel bicycles are a subset of single speed bicycles, however it is possible to have a multi geared fixed gear bicycle. Fixed gear bicycles do not allow the rider to coast without pedaling while a single speed freewheel bicycle does. Fixed gear bicycles simply lack any sort of ratchet mechanism that allows the pedals to coast independently of the drive wheel. Both types of these bicycles are, in general, truly single speeds; however, fixed gear bicycles require distinct skills of their riders.

Advantages and disadvantages versus multi-speed bicycles

Advantages

A single-speed bicycle is generally cheaper, lighter, and mechanically simpler than its multi-geared equivalent. Without derailleurs or other gearing systems, there are fewer parts on the bicycle that require maintenance. Replacing gears and chains on a single-speed bicycle is significantly cheaper. This is particularly advantageous when biking in muddy and gritty conditions which would wear out the expensive components of a geared bike.

The drivetrain efficiency of a single-speed can be greater than today's typical multi-geared bicycles. A straight chainline, lack of chain drag from rear derailleur jockey pulleys, and lack of chainrings, ramps and pins all improve efficiency. As a single rear cog takes less space than the typical seven to ten cogs present on most multi-geared rear cassettes, rear wheels can be built with little or no dish, which is inherently stronger.

Single-speed bicycles are characterized by a simple and uncluttered look.

Disadvantages

smaller range of efficient speeds at which the bicycle can be pedaled
typically lower top speed of bicycle
banned from some races and other bicycle events

Types of single speed bicycles

Typically a reference to a single speed bicycle invokes the idea of a single speed roadbike, generally descended from track-racing bicycles and sharing a number of stylistic and functional similarities. However, mountain bicycles, road bicycles, cyclo-cross bicycles, and hybrid bicycles can be made as or changed into a single speed. Mountain bike single speeds designed for trail riding often have a relatively low, or easy and slow, gear ratio. This allows them to climb hills and deal with obstacles and gradients better. Single speed bicycles designed for road riding typically have higher, or harder and faster, gear ratios.

Single speed bicycles and fixed gear bicycles are popular with bicycle messengers for their reliability and durability. Depending on the situation, a messenger may prefer a mountain bike based single-speed, which can be an urban tank, able to roll over almost any obstacle, or a road bike-based single-speed, which is fast and light.

Statements by cycling industry representatives and journalists fueled the perception that major bicycle manufacturers discouraged modern single speed bicycles. However, increased popularity of the single speed has resulted in the design, marketing, and production of many models. In the United States market, bicycle companies Bianchi, Cannondale, KHS, Kona, Raleigh, Giant, Specialized, and Trek all have recently produced and marketed single speed bicycles.

Single speed mountain bikes are typically constructed with no suspension (fully rigid) or front suspension forks. However, as single speed bicycle production by major manufacturers has become more common, a limited number of fully suspended single speed mountain bikes have been produced. However the popularity of "full-suspension" single speeds has been limited by the general impression that the increased weight and complexity of a fully suspended frame runs counter to the "light and simple" image sought by many single speed riders.

Chain tensioning

Single-speed bicycle builders have devised a variety of methods for producing and maintaining the proper chain tension. The most common method is horizontal rear dropouts or track ends. These allow the rear wheel to be moved fore or aft as necessary. Another method uses an eccentric mechanism either in the bottom bracket^[1] or in the rear hub.^[2] If neither of these are an option, when working with an existing frame not originally designed for single-speed use for example, some kind of idler pulley, such as the Surly Singlelator^[3] , can be used to take up chain slack. Finally a magic combination of chainring, cog, and chain length may work well enough until the chain wears.

The last two years have seen several prototypes of singlespeed bikes using belt drives in place of chains - these offer increased efficiency and are less prone to changes in chainlength as they do not stretch or wear to the same degree. However the need to split the rear chainstay in order to fit a new belt is the major drawback - although several major manufacturers are examining the feasibility of such belt drive systems and how they might be integrated with hub based gears like the Rohloff system.

References

^ "Bottom Bracket Eccentrics & Shells". Retrieved 2007-10-19.
^ "The White Industries ENO Single Speed Fixed/Free Hubs". Retrieved 2007-10-19.
^ "Singlelator". Retrieved 2007-10-19.

External links

[Wood-1] "Bottom Bracket Eccentrics & Shells". Retrieved 2007-10-19.

[White-2] "The White Industries ENO Single Speed Fixed/Free Hubs". Retrieved 2007-10-19.

[Surly-3] "Singlelator". Retrieved 2007-10-19.

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