A fixed-gear bicycle or fixed wheel bicycle, is a bicycle without the ability to coast. The sprocket is screwed directly on to the hub and there is no freewheel mechanism. A reverse-thread lockring is usually fitted to prevent the sprocket from unscrewing. Whenever the rear wheel is turning, the pedals turn in the same direction. By resisting the rotation of the pedals, a rider can slow the bike to a stop, without the aid of a brake. A fixed gear bicycle can even be ridden in reverse.
Most fixed gear bicycles only have one gear ratio. Some have a sprocket on each side of the rear hub, giving the choice of using one of two different gear ratios. Such a hub may have a fixed gear on each side (double-fixed) or a fixed gear on one side and a freewheel gear on the other (fixed-free). To change gear, it is necessary to remove, reverse and refit the rear wheel. Typically, the number of teeth on the sprockets will differ by one or two, for example 19 teeth on one side and 17 on the other, making the latter gear some 11 or 12% higher than the former (for the same chainring).
The track bicycle is a form of fixed-gear bicycle used for track cycling in a velodrome. But since a "fixed-gear bicycle" is just a bicycle without a freewheel, a fixed-gear bicycle can be any type of bicycle.
Traditionally, road racing and club cyclists would use a fixed wheel bicycle for training during the winter months, generally using a relatively low gear ratio, believed to help develop a good pedalling style. In the UK until the 1950s it was common for riders to use a fixed wheel for time trials. The fixed wheel was also commonly used, and continues to be used in the end of season hill climb races in the autumn. A typical clubmen's fixed wheel machine would have been a "road-path" or "road/track" cycle. In the era when most riders only had one cycle, the same bike when stripped down and fitted with racing wheels was used for road time trials and track racing, and when fitted with mudguards (fenders) and a bag it was used for club runs, touring and winter training. However by the 1960s multi-gear derailleurs had become the norm and riding fixed wheel on the road declined over the next few decades. Recent years have seen renewed interest and increased popularity of fixed wheel cycling in the UK.
In urban North America recently the popularity of fixed gear bicycles have attained something of a cult status, and even discernible regional aesthetic preferences in terms of finish and presentation of such bicycles have appeared. The rise in popularity of fixed-gear bicycles in the mid-2000s, complete with affectations such as spoke cards (gathered from "alleycats" typically), is attributed to bicycle messengers. Some messengers disparagingly refer to persons sporting these affectations as 'fakengers,' 'posengers' or 'hipsters'.
Dedicated fixed-gear road bicycles are being produced in greater numbers by established bicycle manufacturers. They are generally low in price, and characterized by a more forgiving, slacker road geometry, as opposed to the steeper, more aggressive geometry of track bicycles. These too are made in increasing numbers at budget, or entry-level price and quality-points.
A fixed-gear bicycle is particularly well suited for track stands, a manoeuver in which the bicycle can be held stationary, balanced upright with the rider's feet on the pedals.
A subset of fixed gear track bike riding is emerging from urban youth, often associated with Hipster (contemporary subculture), with roots in modern skateboarding and Freestyle BMX. Track bike tricks are largely unexplored and like the sport's precursors, have an overwhelming appreciation for style and originality. "Fixies" are also used for increased performance.
Many people who ride fixed-gear bicycles simply find it more enjoyable than or as an alternative to riding bikes with freewheels. Although the bike has only one gear, the lighter weight of a fixed-gear bike over its multi-speed freewheel equivalent can provide increased performance. Although the rider cannot change to a lower gear, climbing hills on a fixed gear is easier than with a multi-speed freewheel because it is easier to maintain momentum as the cranks are pushed through the dead centers by the chain, though this could be because a fixed bicycle is lighter than its multi-speed freewheel equivalent. In slippery conditions some riders prefer to ride fixed because the transmission gives feedback on back tire grip.
Descending is more difficult as the rider must spin the cranks at a very high speed (sometimes at 150rpm or more), or use the brake(s) to slow down. Nevertheless, the enforced fast spin when descending is said to increase "souplesse" (a French word roughly meaning suppleness), which improves pedaling performance on any type of bicycle.
Riding fixed is generally considered to encourage a more effective pedaling style, which translates into greater efficiency and power when used on a bicycle fitted with a freewheel.
When first riding a fixed gear, a cyclist used to a freewheel has a tendency to try to coast now and again, particularly when approaching corners or obstacles. Since freewheeling is not possible, this can lead to anything from a 'kick' to the trailing leg, up to a loss of control of the bicycle.
A rider can also lock the rear wheel and skid to slow down or completely stop on a fixed-gear bicycle, a maneuver sometimes known as a skid stop. It is initiated by unweighting the rear wheel while in motion (and usually lifting it off the ground slightly) by shifting the rider's weight forward and pulling up on the pedals using clipless pedals or toe clips. The rider then stops turning the pedals, thus stopping the drivetrain and rear wheel, while applying his or her body weight in opposition to the normal rotation of the pedals. When the rear tire again contacts the ground the rear wheel will skid, which acts to slow the bike. The skid can be held until the bicycle stops or until the rider desires to continue pedalling again at a slower speed. The technique requires a little practice and using it while cornering is generally considered dangerous. As with the technique of resisting the pedals, the maximal deceleration of this method of slowing is also significantly lower than using a front brake. A wet surface further reduces the effectiveness of this method, almost to the point of not reducing speed at all.
Brakeless fixed riding has an almost cult status in some places, based on the perception by some riders of the experience of riding in a state of intense concentration or 'flow' where brakes are thought not to be needed.
Other riders dismiss riding on roads without brakes as an unnecessary affectation, based on image rather than what is practical when riding a bicycle. Furthermore, riding brakeless may jeopardize the chances of a successful insurance claim in the event of an accident and, in some jurisdictions (including the UK ), is against the law. It also greatly increases stress on the knees which can lead to injury. Some will have one (usually front) brake for emergencies, for descending steep hills, for safety in the event of a broken or derailed chain, to comply with traffic law, or to prevent knee injury. Others will have two brakes for better control in hills, for slippery road conditions, or for use in the event of a broken or thrown chain, broken brake or brake cable.
In the United States, fixed-gear bikes without hand brakes are illegal in many places. Fixed-gear sidewalk bikes -- the U.S. Consumer Product Safety Commission's term for one with a seat height of no more than 25 inches adjusted to its highest position, and no free wheel -- are not required to have brakes if they bear a permanent label visible from 10 feet displaying the words "No Brakes." The same label must be displayed prominently on promotional display material and shipping cartons.
In the UK, the Pedal Cycles Construction and Use Regulations 1983 requires that pedal cycles 'with a saddle height over 635mm to have two independent braking systems, with one acting on the front wheel(s) and one on the rear' . It is commonly thought that a front brake and a fixed rear wheel satisfies this requirement.
For a variety of reasons, many cyclists choose to convert freewheel bicycles to fixed gear. Frames with horizontal dropouts will be straightforward to convert, frames with vertical dropouts less so. One method is to simply replace the rear wheel with a wheel that has a track/fixed hub. Another is to use a hub designed to be used with a threaded multi-speed freewheel. Such a hub will only have the normal right-handed threads for the sprocket and not the reverse threads for the lockrings used on track/fixed hubs. There is a slight possibility that the sprocket on a hub without a lockring will unscrew while back pedalling. Even if a bottom bracket lockring is threaded onto the hub along with a track sprocket, because the bottom-bracket lockring is not reverse threaded, the possibility still exists that both the sprocket and locknut can unscrew. Therefore it is recommended to have both front and rear brakes on a fixed-gear bicycle using a converted freewheel hub in case the sprocket unscrews while back pedaling. It is also advisable to use a thread locking compound such as manufactured by Loctite for the sprocket and bottom bracket lockring. The rotafix (or "frame whipping") method may be helpful to securely install the cog.
Bicycles with vertical dropouts and no derailleur require some way to adjust chain tension. Most bicycles with horizontal dropouts can be tensioned by moving the wheel forward or backward in the dropouts. Bicycles with vertical dropouts can also be converted with some additional hardware. Possibilities include:
Separate chain tensioning devices such as the type which are attached to the dropout gear hanger (commonly used on single speed mountain bikes) cannot be used because they will be damaged as soon as the lower part of the chain becomes tight.
Additional adjustments or modification may be needed to ensure a good chainline. The chain should run straight from the chainring to the sprocket, therefore both need to be the same distance away from the bicycle's centerline. Matched groupsets of track components are normally designed to give a chainline of 42mm, but conversions using road or mountain bike cranksets often use more chainline. Some hubs, such as White Industries' ENO, or the British Goldtec track hub, are better suited to this task as they have a chainline greater than standard. Failure to achieve good chainline will at best lead to a noisy chain and increased wear, and at worst can throw the chain off the sprocket. This can result in rear wheel lockup and a wrecked frame if the chain falls between the rear sprocket and the spokes. Chainline can be adjusted in a number of ways, which may be used in combination with each other:
There are many forms of competition using a fixed gear bike, including most track racing. Bike messengers and other urban riders may ride fixed gear bicycles in alleycat races, including New York City's famous fixed-gear-only race Monstertrack alleycat. Some riders in a hill climb also use fixed wheel bikes.