A velodrome is an arena for track cycling. Modern velodromes feature steeply banked oval tracks, consisting of two 180-degree circular bends connected by two straights. The straights transition to the circular turn through a moderate easement curve.
Banking in the turns, called superelevation, allows riders to keep their bikes relatively perpendicular to the surface while riding at speed. When traveling through the turns at racing speed, which may exceed 85 km/h (about 52 mph), the banking attempts to match the natural lean of a bicycle moving through that curve. There is no centrifugal effect 'trying' to tilt the bicycle outward: the net normal force is acting on the tires through the riding surface.
Riders are not always traveling at full speed or at a specific radius. Most events have riders all over the track. Team races (like the madison) have some riders at speed and others riding more slowly. In match sprints riders may stop. For these reasons, the banking tends to be 10 to 15 degrees less than physics predicts. Also, the straights are banked 10 to 15 degrees more than physics would predict. These compromises make the track ridable at a range of speeds.
From the straight, the curve of the track increases gradually into the circular turn. This section of decreasing radius is called the easement spiral or transition. It allows bicycles to follow the track around the corner at a constant radial position. Thus riders can concentrate on tactics rather than steering.
Bicycles and track design
Bicycles for velodromes have no brakes. They employ a single fixed rear gear, or cog, that does not freewheel. This helps maximize speed, reduces weight, avoids sudden braking while nevertheless allowing the rider to slow by pushing back against the pedals.
Modern velodromes are constructed by specialised designers. The Schuermann architects in Germany have built more than 125 tracks worldwide. Most of Schuermann's outdoor tracks are made of wood trusswork with a surface of strips of the rare rain-forest wood Afzelia. Indoor velodromes are built with less expensive pine surfaces. Other designers have been moving away from traditional materials. The 1996 Atlanta Olympics saw the introduction of synthetic surfaces supported by steel frames.
The track is measured along a line 20 cm up from the bottom. Olympic standard velodromes may only measure between 250 m and 400 m, and the length must be such that a whole or half number of laps give a distance of 1 km. Others range from 133 m to 500 m, although 250m is the most popular and the length used in major events. The velodrome at Calshot Spit, Hampshire, UK is only 142 m because it was built to fit inside an aircraft hangar. It has especially steep banking. Forest City Velodrome in London, Ontario, Canada, is the world's shortest at 138 m. It was built to fit a hockey arena. Like Calshot, it has steep banking.
Many old tracks were built around athletics tracks or other grounds and any banking was shallow. The smaller the track, the steeper the banking. A 250 m track banks around 45°, while a 333 m track banks around 32°.
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