Modern bicycle inner tubes utilise two types of valve stems for tire inflation. However, older bicycles and bicycles manufactured for use in Asian countries often came with a third valve stem type. Common valves, Schrader and Presta, often appear in the United States, but the less common Woods valve rarely surfaces anymore. Most bicycle valves attach directly to tubes, but newer tubeless bicycle tire designs typically utilise specialised Presta valves attaching directly to the bicycle rim.
Schrader Valve Stems
Schrader valve tubes come equipped with a valve stem often called an "American valve." Schrader valves require the depressing of an internal spring-loaded pin to insert or remove air. Schrader valves exhibit the same design and function as normal car tire valve stems, according to bicycle shop Bonthrone Bikes website. Schrader valve stems often see use in the American plumbing industry as well. Schrader valve stems typically outweigh smaller Presta valves, but do not require a special adaptor or pump for airing bicycle tires at most American gas stations or bicycle shops. Most inexpensive and department store brand bicycles come equipped with Schrader valve tubes. Schrader valve caps keep dirt from clogging the valve.
Presta Valve Stems
Presta valve stems, smaller and lighter than traditional Schrader valves, often appear on tubes installed in more expensive or race ready bicycles in the U.S. Rims drilled for Presta valve stems, commonly called "French valves," require the drilling of a 21/64 inch hole to accept Schrader valves, according to bicycle mechanic and prolific cycling industry cataloger the late Sheldon Brown. Presta valves require the unscrewing of a small nut attached to the pin sealing the valve before air can enter or exit the tube. Presta valve adaptors, typically small threaded brass fitting, allow for the filling of Presta valves with American Schrader valve pumps or hoses. Presta valve caps protect delicate tube rubber while shipping, but serve no function while riding.
Woods Valve Stems
Woods valve stems, commonly called "Dunlop valves," often appeared on older bicycle tubes decades ago. Bonthrone Bikes recommends replacing these ancient tubes immediately as the tubes likely will fail soon if they hold air at all. Woods valves begin roughly as the size of Schrader valves at the base yet taper to nearly the thin size of Presta valves at the tip. Generally, pumps that air Presta valves also air Woods valves. Some patch kits still include small rubber tubes along with other tube patch necessities such as glue or sandpaper. These small rubber tubes replace the often-decayed inner rubber fitting found inside Woods valve stems. Woods valve tubes, though rare, occasionally find their way inside bicycles manufactured and distributed in Asian countries.