Tube

INNER TUBES

There are three types of valve stems on bicycles, Schrader, Presta and Woods (Dunlop).

SCHRADER

The Schrader or “American-type valve” is common on cars and motorcycles. It is also found on many bicycles. The valve stem is approximately 8mm (5⁄16 inch) in diameter. The valve core consists of an internal spring plunger to assist in shutting the valve after inflation.  The length of the valve can vary and should be longer for tall or deep rims.

PRESTA

The Presta or French-type valve is common on mid- and higher-priced road bikes and on higher-priced mountain bikes. Presta stems are nominally 6mm in diameter and thinner compared to the Schrader valves. At the top of the Presta stem is a small valve locknut, which must be unthreaded before air can enter the tube.

Some brands of Presta tubes use a valve shaft that is fully threaded and usually include a locking nut or ring. These come with an extra locking nut or ring. Loosen the ring by hand and remove it before installing the tube. Install and fully inflate the tube. Then install the lockring and snug only by hand. When deflating the tube, loosen and remove the nut first.

Some makes and models of Presta inner tubes use a removable valve core. Inspect the end of the valve for two wrench flats. Usea small adjustable wrench to secure or remove the core.

Inner tube valve stems are available in different lengths. Rims with a very tall cross section require longer valve stems (60 mm or 80 mm). There are valve extenders available that screw onto the Presta valve and allow the tube to be inflated (figure 2.38). If the inner tube uses a removable valve core, use an extension that screws into the valve’s inner threads. There are also designs that are simply a tube to lengthen the stem but do not permit the Presta valve locking nut to be secured. If the locking nut cannot be closed, the valve may leak. Extenders that do not allow the valve nut to be tightened may allow the tube to leak slowly.

The wheel rim valve hole should match the valve of the tube. If a rim has been made with the smaller valve hole for Presta valves, it can be typically drilled and enlarged safely to the 8 mm size by using an 11⁄32 inch (8.5 mm) hand drill. After drilling, use a small round file to remove any sharp edges. Rims that are less than 15 mm outside width should not be drilled. It is also possible to use the smaller Presta valve in a rim intended for the larger Schrader by using an adapter sleeve.

WOODS/DUNLOP

A third valve type is the “Woods” or Dunlop valve. These are seen on less expensive bikes outside the United States. The stem looks like a combination of a Schrader and a Presta stem. The top of the stem is narrow, with a large locking ring under it, and then the main shaft. 

To deflate the Dunlop valve, partially unthread the nut. Pull on the tip of the valve if air is not already escaping. Remove the nut fully after the inner tube is deflated. Remove tire and tube as any other.

To inflate the Dunlop valve, use a Presta compatible pump head. Simply engage the head and inflate. Remove the head.  There is no need to unthread the locking ring.

The tube should match the tire size diameter closely. However, tires that are close in bead diameter may use the same inner tube. For example, an inner tube for an ISO 630 tire (27-inch) will also fit an ISO 622 (700c) tire.

The inner tube should also match the tire width, but, because inner tubes are elastic, one inner tube may fit a range of tire widths. If the inner tube is too narrow for the tire width, it will become very thin when inflated inside the tire body. This will cause it to be more susceptible to punctures and failures. If the tube is too wide for the tire, it will be difficult or impossible to properly fit inside the tire casing and seat in the rim. Part of the tube may stick out of the tire and blow out when the tire is fully inflated.