Track bicycle
From Wikipedia, the free encyclopedia
A track bicycle is a type of fixed-gear bicycle specially designed for track cycling in a velodrome. Unlike road bicycles, used for road cycling, they lack multiple gears and brakes, having a single fixed gear ratio and no freewheeling mechanism. Tires are narrow, and as the track surface is very smooth there is no need for shock absorption, tires can be inflated to very high pressures well beyond those used in road cycling to minimise the rolling resistance caused by friction. Very lightweight tubular tyres can be used as there is almost no risk of punctures. (For grass-track events, the tires would have 'knobs' intended to minimise the potential for skidding.)
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[edit] Frame design
The design of track frames is usually very specific to its use. In general high rigidity is more important than low weight. Frames intended for sprinting are generally made as rigid as possible, while those made for general racing or longer events are made as aerodynamic as possible.
The International Cycling Union sets certain limits on the aerodynamic shapes of track frames, including the maximum and minimum diameter of tubes and overall dimensions of the bicycle.
Frame materials are wide-ranging, including steel (the traditional material for track bikes), aluminium, carbon fibre, or titanium, with carbon fibre being the most common on the professional or elite level. Steel is the most common material on track frames used by urban, road and non-track riders which are not ridden on a velodrome. Starting in 2004 carbon fiber has become more popular for non-frame components such as Easton's carbon fiber track bar, which is claimed to be fully a pound lighter than a traditional steel track bar.
Additionally, the geometry of a track frame differs from that of a road frame, and many frames are designed for specific track events (an omnium frame refers to one that is designed for general track racing). Those attributes common to most track frames include a higher bottom bracket for additional cornering clearance, steeper seat tube for a more forward and aerodynamic position, steeper head tube for more responsive steering, and less fork rake for more stable steering at high speeds. Typical track bicycle frames use 120 mm spacing for the rear hub, and have horizontal backwards facing rear ends (track ends) instead of vertical dropouts for adjustment of chain tension. This is 10 mm narrower than modern road bicycle frames intended for use with multiple gears.
[edit] Gears
Since track bicycles have a fixed gear, the choice of gear ratio is very important. At its basic level, a change in gearing is a trade-off of acceleration versus top-end speed. A lower ratio allows quicker acceleration, or 'jump.' This can be crucially important in races where getting a gap on an opponent can be the deciding factor in the race. On the other hand, a big gear makes it easier to sustain a higher top-end, which is paramount in pursuiting/time trialing, but also important in standard scratch/points races in which the pace will be high.
Ideally, in a mass-start race, the cyclist will find a ratio that balances these two requirements. Without a good jump the rider risks opponents opening a gap when they jump to break away; without a good high end the rider will be unable to get around opponents when the pace stays high.
In order to achieve both top-end speed and jump, track cyclists develop very high leg speed and are well-trained to maintain a high cadence smoothly. This allows them to go faster with a smaller gear.
Long distance record attempts, for example the hour record typically use very large gearing combinations such as 52x12 or 55x14. Ondřej Sosenka used a combination of 54x13 with 190 mm long crankarms to set the 2005 hour record.
[edit] Chain
There are two common widths of single speed and fixed gear bicycle chains, 1/8 inch and 3/32 inch. Most track bicycles use the wider, heavier 1/8 inch chain (also used by BMX bicycles and old-fashioned roadsters). 1/8 is standard for track use and all chains marketed for track use are 1/8. However because 3/32 chainrings and chains are much more common, and perhaps 3/32 inch chains are slightly lighter, some track riders use a 3/32 inch chain, which is the same type used on 7 and 8 speed derailleur equipped road or mountain bikes. For the best results, the chainring, sprocket and chain should all be the same width. Although an 1/8 inch chain will work on a 3/32 chainring or sprocket, it is not ideal. A 3/32 inch chain will not work on a 1/8 chainring or sprocket. Most common track sprockets, e.g. Shimano Dura-Ace Track, are available in both widths. Because they do not need to shift from sprocket to sprocket, track chains still use a "full bushing" design which allows very little sideways flex but can be stronger. All bicycles with derailleur gears use "bushingless" chains which can flex substantially, making gear changing possible.
