A tire valve stem is a simple device that allows air to enter a tire from a pump, and the stem then self-seals to hold air inside. Valves come either integrated with the tire, as in an automobile tire, or connected to a rubber liner tube, as with bicycle tires. Tire valves are made from rubber, plastic and metal, and the rubber will sometimes deteriorate or be damaged, causing leaks to develop. There are three main valve types.
Schrader valves are common in the United States and are sometimes called American valves. They are a universal style that makes it easy for them to be used in other applications or in other parts of the world easily. Schrader valves are used in almost all American-made car and truck tires and bicycle tires, and can therefore be filled at almost any gas station compressor or with easily found hand pumps. These typically have a large diameter and are easy to fill and seal.
Presta valves have a smaller diameter than Schrader valves and are most commonly used with bicycle tires. Also known as French valves, these are streamlined to make them lighter and more aerodynamic. This makes them ideal for bike racing and they are used almost exclusively in competition cycling. Presta valves work well with more narrow tires, and can therefore allow for narrower rims, tighter wheel spokes and a stronger overall wheel.
Dunlop valves are not as common as Schrader and Presta valves. Also known as English valves, these were very popular for a short time in Great Britain but have been largely replaced by Presta for biking and Schrader for automobiles. They are still used in some countries, including Japan, the Netherlands and Germany, and most commonly on lower-priced items. Due to their similarity to Presta valves, Dunlops will use Presta pumps and tire gauges.
Tire valves and their caps work together to guarantee good tire pressure, and for that reason, a properly fitting cap should always be used. High-quality caps help contain air pressure and can even help a tire survive for a short time if a valve fails. Some caps come with rubber seals to safeguard against air leaks and moisture that may corrode valve parts or freeze in cold weather, causing damage to the inner parts of the valve. If a cap is lost or damaged it should be replaced as soon as possible.
The amount of air within a tire is known as the air pressure. The proper level is determined by the manufacturer and is often printed on the tire. Leaks of any kind will slowly reduce the pressure and affect performance of the tire. Damaged valves will often cause an almost immediate and noticeable loss in pressure from air loss. Tires should be checked regularly with an accurate tire pressure gauge.
