Fixed-gear bicycle

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A fixed gear bicycle

A fixed-gear bicycle or fixed wheel bicycle, is any bicycle without a freewheel and usually only one gear ratio. The sprocket is attached to the hub without a freewheel mechanism, usually secured by a reverse-thread lockring.

Because there is no freewheel mechanism, fixed gear bicycles cannot coast. Whenever the rear wheel is turning, the pedals turn in the same direction. By resisting the forward motion of the pedals, a rider is able to slow the bike to a stop, without the aid of a brake. They can also be ridden in reverse, although the forward-oriented geometry of any bicycle makes this more of a stunt than a practical technique.

Most fixed gear bicycles only have one gear ratio. Some fixed gear bicycles have a sprocket on each side of the hub, commonly referred to as a flipflop hub, giving the choice of using two different gear ratios. To change gear, the rider has to stop, remove, turn around and refit the rear wheel. If the same chain is used in both positions, the difference between these two gears will be small. In the past Sturmey Archer made multi speed fixed hub gears which can change gear whilst riding.

1 Uses
2 Brakes
3 US and British English Usage
4 Conversion
5 Competition
6 See also
7 External links

[edit] Uses

A fixed / freewheel rear hub

One form of fixed-gear bicycles is the track bicycle, used for track cycling in a velodrome. Since a "fixed-gear bicycle" is just a bicycle without a freewheel, it can be any variety of bicycle including road racing, touring, commuting, or off road bicycles. Since a track bicycle always has a fixed gear or fixed wheel, a "fixed-gear bicycle" is more often used to refer to bicycles that are used on the road.

Traditionally, road racing and club cyclists would use a fixed gear or fixed wheel for training during the winter months, generally using a relatively low gear ratio, it was believed that it would help to develop a good pedalling style. In the UK up to the 1950s it was common for riders to use a fixed wheel for time trials, although by the 1960s multi-gear derailleurs had become the norm and riding fixed wheel on the road declined over the next few decades. However in the UK in the last few years there has been a renewed interest and increased popularity of fixed wheel riding.

Recently the popularity of fixed gear bicycles in the USA has been on the rise, particularly in metropolitan centers such as New York, Chicago and San Francisco, where they have attained something of a cult status, and even discernible regional aesthetic preferences in terms of finish and presentation of such biycles.

Dedicated fixed-gear road bicycles are being produced in greater and greater numbers by established bicycle manufacturers, as the popularity of this type of cycling increases. They are generally low in price (averaging in the region of $500), and characterized by 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.

Fixed-gear bicycles are also used in cycle ball and artistic cycling. Riders in artistic cycling often exploit the fixed gear in unicycle-type moves and in riding backwards.

A fixed-gear bicycle is uniquely suited for a maneuver known as a track stand, in which the bicycle can be held stationary, balanced upright with the rider's feet on the pedals.

Fixed gear bicycles are ridden by cyclists (including bicycle messengers) for many reasons, in particular their light weight, simplicity, and low maintenance. Another reason cited by messengers for their popularity is their theft-deterrence: riding away on a stolen fixed-gear bicycle is difficult if the thief does not have previous experience riding one. Finally, many people who ride fixed-gear bicycles simply find it more enjoyable than riding bikes with freewheels.

[edit] Brakes

Because it is possible to slow down or stop a fixed-gear bike by resisting the turning pedals, some riders think brakes are not strictly necessary. However, since the rider can apply braking force only to the rear wheel, the maximal deceleration is significantly lower than on a bike equipped with a front brake. As a vehicle brakes, weight is transferred towards the front wheel and away from the rear wheel, decreasing the amount of grip the rear wheel has. Shifting the rider's weight aft will increase rear wheel braking efficiency, but normally the front wheel might provide 70% or more of the braking power when braking hard.

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 skip 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, and that it is 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. Some will have one (usually front) brake for emergencies, for descending steep hills, for safety in the event of a broken or derailed chain, and to comply with traffic law. UK law requires cycles to have two separate brakes, and the fixed wheel counts as one brake. Others will have two brakes for better control in hills, for slippery road conditions, or for use in the event of a broken brake or brake cable.

In the United States, fixed-gear bikes without brakes are illegal in many places. Laws in most states where fixed-gear riding is popular -- including New York, California, Maryland and Oregon -- require that bicycles be equipped with a brake that enables the operator to make the braked wheels skid on clean, dry pavement. Still, fixed-gear cyclists and lawyers in those states argue that the rider should count as the "brake" if he or she is able to achieve the same effect. In regulatory terms, the bikes fall in a gray area. The U.S. Consumer Product Safety Commission says track bicycles are "designed and intended for use in a competition." They are exempt from federal requirements for standard bicycles, which call for bikes to have brakes at least in the rear. Fixed-gear sidewalk bikes -- the commission's term for one with a seat height of no more than 25 inches adjusted to its highest position, and no free wheel -- aren't 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.

[edit] US and British English Usage

"Fixed gear" is the standard term in the US whilst "fixed wheel" is used in the UK. The confusion comes about because "fixed", "gear" and "wheel" can have more than one meaning in this context. "Fixed" can mean not able to freewheel (coast), it can also mean not variable. "Gear" can refer to the sprocket or to a gear ratio. In the US, "fixed-gear" is used to mean the gear (sprocket) is attached to the hub without a freewheel. In the UK, "fixed-wheel" is the normal term, meaning the opposite of freewheel, whereas fixed gear usually means one gear (gear ratio).

[edit] Conversion

Many companies sell bicycle frames designed specifically for use with fixed-gear hubs. A fixed-gear or track-bike hub includes special threads for a lockring that tightens in the opposite (counter-clockwise) direction compared with the sprocket. This ensures that the sprocket cannot unscrew when the rider "backpedals" while braking.

But, 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 whilst 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 pedalling. It is also advisable to use a thread sealer such as manufactured by Loctite for the sprocket and bottom bracket lockring.

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:

An eccentric hub or bottom bracket allows the off center axle or bottom bracket spindle to pivot and changing the chain tension. See ENO Fixed/Free hubs listed in the external links.
A "Ghost" or "floating" chainring. An additional chainring placed in the drive train between the driving chainring and sprocket. The top of the chain moves it forward at the same speed that the bottom of the chain moves it backwards, giving the appearance that it is floating in the chain.
A "Magic gear". With some math you can calculate a gearing ratio to fit a taut chain between the rear dropout and bottom bracket. Having a chain half link available will double your chances of finding a "magic gear."

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 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.

[edit] Competition

There are many forms of competing with a fixed gear bike. One type of competition is a track stand competition, in which the riders compete in five minute intervals to see which rider can keep their balance the longest rocking back and fourth. Each five minute interval an apendage is removed, starting with the hands and then moving to the feet. Another is skidding. Bike messengers may ride fixed gear bicycles in Alleycat races. Some riders in a hill climb also used fixed wheel bikes.