Air in the inner tube of your bicycle tires is essential to keep the rim off the ground. The valve acts as a gateway to pressuring the inner tube of the tire. Bicycle tire valves have been in use for more than a century, and a peek at the innards of a tire valve shows the ingenuity of their Victorian-era inventors.
Types
Schader and Presta valves are the ones most commonly seen on bicycle tires. Schraders, identical to automotive tire valves, are 8 mm thick and are found on children's bikes and inexpensive hybrid and mountain bikes. The slender Prestas, 6 mm thick, are standard on road racing bicycles and bicycles in Europe. To convert a Presta rim to a Schrader rim, drill out the rim with a 21/64 inch bit, online bike mechanic Sheldon Brown advises. The Woods or Dunlop valve, rarely seen in the United States, was formerly used in the United Kingdom and Asia and looks a bit like a cross between a Schrader and a Presta.
Features
The Schrader valve of a rubber bicycle-tire tube consists of a metal cylinder, which accepts an air-pump chuck, covered with a rubber tube vulcanized to the inner tube of the tire. Prestas feature a threaded metal stem with a nut to hold the valve against the rim. A built-in valve cap needs to be turned counterclockwise to open the valve and manually closed to avoid a slow leak. Schraders feature a pin head pushed up by a spring that a button in the chuck depresses to allow the entry of air.
Function
Valves are essential to allow air under pressure to enter the bicycle tire tube and to prevent its escape. A checking mechanism in the valve requires a fixed amount of pressure to open and allow the air to be pumped in the tube through passages in the body of the valve. Cycling author John Forester notes in "Effective Cycling" that the design of a Presta locks in air as soon as the air-pump chuck is removed, while the Schrader, intended for use with air compressors, allows a fair amount of air to escape when the chuck is applied and when it is removed.
History
In 1893, August Schrader, a German immigrant to New York, and his son, George, developed their eponymous valve, which is still going strong in its original form. Three years later, they patented the cap that keeps dirt out of the valve. The Presta valve's origins seem more difficult to pin down, given only speculative information available on bike forums on this topic. The Woods valve was in widespread use throughout Europe by the 1920s, according to Henry Clemens Pearson's 1,300-page tome, "Pneumatic Tires, Automobile, Truck, Airplane, Motorcycle, Bicycle," published in 1922.
Benefits
Inner tubes with Schrader valves are easy to obtain in the United States, can be inflated at gas stations and feature a more rugged design suitable for children's bikes, writes Luc Lacasse, an engineer and mountain biker with a focus on wheels, on his My Wheels and More online site. Presta valves are more aerodynamic, given their smaller port holes and the fact they permit slimmer rims. They also leak less and are easier to inflate.
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