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. 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 single speed mountain bicycles. The fixed-gear single-speed bicycle is the most basic type of bicycle. A fixed-gear bike does not have a freewheel mechanism to allow coasting. Advantages[edit] 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 making this type of cycle useful for city commuting in all weather. The drivetrain efficiency of a single-speed can be greater than todays 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. Disadvantages[edit] As the single-speed bicycle lacks alternative gearing ratios, it is less versatile, as it cannot be pedaled efficiently outside of its single gearing range. Without lower gearing options, the single speed bicycle is generally more difficult to pedal uphill. Conversely, its dedicated gear ratio also limits top speed, and is slower than a multi-geared bicycle on flat or descending terrain once bicycle speed exceeds the riders ability to maintain continuing increases in cadence (pedaling revolutions per minute), typically 85–110 rpm. Types of single-speed bicycles[edit] Old racing bicycle, casually converted to single speed. Note the semi-horizontal drop-outs, and redundant second chainring. While track bicycles are always single speed, 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. This typically requires the rider to be more fit or skilled than the average rider in order to traverse the same terrain. 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 roll over many obstacles, or a fast and light road bike-based single-speed. 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 such as Bianchi, Cannondale, Fuji Bike, KHS, Kona, Raleigh, Giant, Specialized, Swobo, Felt, Trek and Niner all have recently produced and marketed single speed bicycles. Because most full suspension frame designs either have a single pivot that is not concentric with the bottom bracket, or a linkage with a variable center of rotation, the distance between the bottom bracket and rear axle varies throughout the suspensions travel. This requires a sprung chain tensioner, similar to a rear derailleur, to be used. Only relatively uncommon frame designs with single pivots that are concentric with the bottom bracket allow the use of more desirable static chain tensioners. Another consideration is the generally increased amount of pedalling while standing up that is inherent to single speed mountain biking, which increases losses from suspension bob and squat. Therefore, full suspension mountain bikes are fairly rare, with hardtails and rigid bikes being much more common.
Posted on: Fri, 03 Oct 2014 10:40:20 +0000
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