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.
Although most fixed-gear bicycles (fixies) are technically single speed, the term single-speed generally refers to a single gear ratio bicycle with a freewheel mechanism to allow it to coast.[1]
Vis-à-vis multi-speed bicycles
A single-speed mountain bike. The frame was modified by replacing the rear drop-outs with track fork ends to allow the chain to be tensioned.
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, making this type of cycle useful for city commuting in all weather. 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 twelve cogs present on most multi-geared rear cassettes, rear wheels can be built with little or no dish.
Disadvantages
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 rider's ability to maintain continuing increases in cadence (pedaling revolutions per minute), typically 85–110 rpm. Compared to a fixed-gear bicycle, a singlespeed is easier to ride downhill and around corners (the inside pedal can be kept up to avoid grounding). However, it does not help the rider pedal around the dead centres like a fixed gear, nor does it allow the fine speed control or easy trackstands that a fixed gear permits. The pawls of a dirty and unmaintained freewheel can also clog, leaving the rider with no drive; this is impossible on a "fixie".
Types of single-speed bicycles
Racing bicycle, once equipped with multiple gears and derailleurs, 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.[2] 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.
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 suspension's 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.
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. Using chain tugs with track ends ensures that optimum chain tension can be achieved with the wheel remaining centered. A similar design, sliding dropouts, uses detachable dropouts that are bolted to the frame through horizontal slots. This allows both quick release or bolt on hubs to be used, or through-axle hubs with the appropriate dropouts. Sliding dropouts usually have set screws that bear on the front of them through the frame to adjust their position for tensioning and wheel alignment. The main advantage of sliding dropouts over track ends is realized when they are used with disc brakes, as the brake caliper mount is part of the left dropout, and thus moves with the dropout, maintaining the hub to caliper distance. Sliding dropouts can also include a derailleur hanger if multi-speed use is desired.
Another method uses an eccentric mechanism either in the bottom bracket[3] or in the rear hub.[4] 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 Singleator[5] or simply a short cage rear derailleur can be used to take up chain slack. As well, finetuning the combination of chainring, cog, and chain length may suffice until the chain develops significant wear.
Throughout the years bicycle designers have produced belt-driven bicycles.[6] While these belts cannot be shifted between gears like a chain, they offer singlespeed or hub geared drivetrains with improved increased wear resistance, quieter operation, and lubrication-free cleanliness. Belts also do not change length during their lifespan in the same way that chains "stretch" or increase in pitch as their link pivots wear. This keeps the pitch of the belt's teeth constant and dramatically decreases wear on gear teeth. Belts have failed to overtake chains in popularity for bicycles because they have historically been less efficient. Also replacement of the one-piece belt requires traditional diamond bicycle frames to have a split chainstay or seatstay.
Chain tensioned without a dedicated tensioner mechanism
Single-speed cycle conversions
Single-speed bicycle builders have converted many former multi-geared cycles into single or fixed gear through the removal of the derailleurs and associated hardware. The simplest conversion uses the existing freewheel/cassette and crankset, the chain being cut to fit the desired gear ratio. However this retains unnecessary weight and the chainline will most likely not be perfect. A more thorough conversion will involve replacing the freewheel with a single-speed one, and re-dishing the rear wheel. On bicycles with vertical dropouts, a chain tensioner is often required to allow the correct tension on the resulting shorter chain.
A very popular "off road" mountain bike gearing, for the 26″ wheel size, is 39:18, approximately a 2:1 gear ratio and 56.35 gear inches, for versatile trail riding. A great "on road" gear ratio, for the 26″ wheel, is 42:17, approximately a 2.5:1 ratio and 64.2 gear inches for versatile tour riding. Many British enthusiasts used to tour on 27–inch–wheeled lightweights on a single fixed–gear of 69 inches before multi–speed gearing became universally popular, though this certainly made for tough work.[7]
A reasonable "road" gear ratio, for the 700 × 28c wheel size a, is 46:17, approximately a 2.7:1 ratio and 71.75 gear inches, for very versatile asphalt riding, and a better lifespan with good road duty.
Fixed-gear setups work especially well with higher 40s chainrings, so the rotation ratio is closer to a wider 3:1, avoiding the tighter ratios, which will spin too fast, especially when descending steep hills.
Note that the larger diameter gear and chain ring, clearly, offers the best longevity, with much better wear characteristics than smaller gear and chain ring sets and less rounding of the teeth, over time.
Flip-flop hubs
Flip-flop, or double-sided hubs are threaded on both sides. Usually one side has a track-type threading (with lock ring), and the other side is threaded for a single-speed standard freewheel. It is possible to find them with track threading on both sides, but not easily. The cyclist can then change gears manually by reversing the drive wheel.
The usual way to use a flip-flop hub is to have a fixed gear on one side, and a single speed freewheel on the other. Ideally, the freewheel sprocket would be one or two teeth larger than the fixed sprocket. This allows for extended hill climbs at a lower ratio than the fixed gear provides. The freewheel in this gear also allows the cyclist to coast on a steep descent.
A tandem bicycle or twin is a form of bicycle designed to be ridden by more than one person. The term tandem refers to the seating arrangement, not the number of riders. Patents related to tandem bicycles date from the mid 1880s. Tandems can reach higher speeds than the same riders on single bicycles, and tandem bicycle racing exists. As with bicycles for single riders, there are many variations that have been developed over the years.
A derailleur is a variable-ratio bicycle gearing system consisting of a chain, multiple sprockets of different sizes, and a mechanism to move the chain from one sprocket to another.
A hub gear, internal-gear hub, internally geared hub or just gear hub is a gear ratio changing system commonly used on bicycles that is implemented with planetary or epicyclic gears. The gears and lubricants are sealed within the shell of the hub gear, in contrast with derailleur gears where the gears and mechanism are exposed to the elements. Changing the gear ratio was traditionally accomplished by a shift lever connected to the hub with a Bowden cable, and twist-grip style shifters have become common.
The crankset or chainset is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel. It consists of one or more sprockets, also called chainrings or chainwheels attached to the cranks, arms, or crankarms to which the pedals attach. It is connected to the rider by the pedals, to the bicycle frame by the bottom bracket, and to the rear sprocket, cassette or freewheel via the chain.
A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust, or simply for aesthetics.
A track bicycle or track bike is a bicycle optimized for racing at a velodrome or outdoor track. Unlike road bicycles, the track bike is a fixed-gear bicycle; thus, it has only a single gear ratio and has neither a freewheel nor brakes. Tires are narrow and inflated to high pressure to reduce rolling resistance.
A fixed-gear bicycle is a bicycle that has a drivetrain with no freewheel mechanism such that the pedals always will spin together with the rear wheel. The freewheel was developed early in the history of bicycle design but the fixed-gear bicycle remained the standard track racing design. More recently the "fixie" has become a popular alternative among mainly urban cyclists, offering the advantage of simplicity compared with the standard multi-geared bicycle.
A fork end, fork-end, or forkend is a slot in a bicycle frame or bicycle fork where the axle of a bicycle wheel is attached. A dropout is a type of fork end that allows the rear wheel to be removed without first derailing the chain.
On a bicycle, the cassette or cluster is the set of multiple sprockets that attaches to the hub on the rear wheel. A cogset works with a rear derailleur to provide multiple gear ratios to the rider. Cassettes come in two varieties, freewheels or cassettes, of which cassettes are a newer development. Although cassettes and freewheels perform the same function and look almost the same when installed, they have important mechanical differences and are not interchangeable.
A freehub is a type of bicycle hub that incorporates a ratcheting mechanism.
A front freewheel or freewheel crank is a freewheel mechanism used on some bicycles which enables the drivetrain of the bicycle to continue spinning while the rider rolls, but stops pedaling, or coasts. Unlike regular bicycles, a front freewheel can make it possible to shift gears using a derailleur while the rider is coasting if paired with a fixed rear hub or a freehub with a slight resistance in the freewheel mechanism, which causes the chain to continue spinning with the wheel rotation.
Bicycle gearing is the aspect of a bicycle drivetrain that determines the relation between the cadence, the rate at which the rider pedals, and the rate at which the drive wheel turns.
A rowbike is an example of a rowing cycle, hybrid fitness/transport machine that combines a bicycle, and a rowing machine. "Rowbike" is a trademark of the Rowbike company. The Rowbike was invented by Scott Olson, the creator of Rollerblade inline skates. "Rowling" is a combination of rowing and rolling, and is sometimes used in place of rowing when describing a Rowbike.
A belt-driven bicycle is a chainless bicycle that uses a flexible belt, typically a synchronous toothed design, in order to transmit power from the pedals to the wheel.
The Honda RN-01 G-Cross is a mountain bike produced by Honda specifically for downhill racing events. Honda is not a manufacturer of bicycles and this bike is not commercially available to the general public. It was introduced in the 2004 racing season by the Team G Cross Honda who competed in the NORBA and Mountain Bike World Cup points series races.
Flip-flop hubs, also called double-sided hubs, are rear bicycle hubs that are threaded to accept fixed cogs and/or freewheels on both sides.
Bicycle drivetrain systems are used to transmit power on bicycles, tricycles, quadracycles, unicycles, or other human-powered vehicles from the riders to the drive wheels. Most also include some type of a mechanism to convert speed and torque via gear ratios.
Mountain bike trials, also known as observed trials, is a discipline of mountain biking in which the rider attempts to pass through an obstacle course without setting foot to ground. Derived from motorcycle trials, it originated in Catalonia, Spain as trialsín and is said to have been invented by Pere Pi, the father of Ot Pi, a world champion motorcycle trials rider. Pi's father had wanted his son to learn motorcycle trials by practicing on an ordinary bicycle.
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