• Posted Mar 26, 2007

Bicycling 101 - Impress your friends. WOW your coworkers. Be smarter than a 5th grader!

Ever been at the bike shop asking for tubes and been caught off-guard when the cool bike shop dude or dudette asks "what type of valves stems do you use?" BUSTED... Your palms get sweaty, your face turns red, you swallow hard and say "I don't know..." This feature will help you answer with confidence and assertiveness. Know your valve stems. Be smarter than the training wheel kid down the block. Be a better cyclist with a mini-Bicycling 101 course.
Valve History... Many valve types have come along since the invention of the pneumatic tire but for bicycles mainly Presta and Schrader remain in use. The Presta valve is the more slender of the two and is slightly more cumbersome to use, having a lock nut instead of a spring to ensure closure. However, these two features have kept the Presta valve in use on many bicycles. In the past, sports and racing bicycles used Presta valves because they are slender and enabled racers to inflate tires with a simple pump with attached chuck (pump head) and no hose. Presta valves are easier to pump than Schrader, because they have no valve spring to overcome. Although a valve depressor for Schrader valves could alleviate this, it would require a check valve, impractical to house in lightweight pump heads. The small diameter of the Presta valve requires a smaller hole in the rim, whose size is important for narrow rims where cross sectional strength of is significantly reduced by a stem hole. In narrow rims, clincher tires also leave insufficient space between tire beads for larger Schrader valves. In contrast Schrader valves are more robust, universally used, and have an easily removable core. Spring closure makes them simpler to use because one needs only to press the inflation chuck onto them at an automobile service station. For hand pumps, a screwed or lever chuck provides the valve depressor. The depressor not only makes inflation easier but is necessary to read back pressure in the tire. Although Presta valves have been made with removable cores, demand is so small that they are uncommon. Removable Presta cores can be identified by two wrench flats on the coarse valve cap threads.
Got A Flat? Get The Correct Tube Valve And Know How It Works Presta-Valve Basics Before you can put air in a Presta valve, you must unscrew its tip. Look closely and you'll see that the valve's tip is knurled to make it easy to turn it by hand. Unscrew it all the way (counter-clockwise) and then press the tip down until some air escapes. This is important because it frees the valve, which usually sticks after being sealed for a while. Until you free it, it can be difficult to impossible to put air into the valve. Here are six other valuable valve facts: 1. Replaceable Presta Cores Some Presta valves have replaceable cores. You can tell if yours is by looking for wrench flats on the sides of the valve just below the tip. A replaceable core is a nice thing if yours gets damaged somehow. However, it's also something to check regularly because if it loosens, you'll develop a slow leak and get flats all the time. The solution is simple, just snug the valve by tightening it with an adjustable wrench (turn clockwise). 2. CO2 Cautions Take extra precautions using CO2 inflators on valves with replaceable cores. The drastic pressure drop as the CO2 leaves the cartridge super-cools the cartridge and adapter. In damp weather, this can freeze the cartridge to the valve. And when you unscrew the adapter, you extract the valve core with it, deflating the tube. To prevent this, after inflation, squirt the valve with some water from your waterbottle to de-ice things and then carefully remove the adapter from the core. 3. Converting Schrader Holes For Presta Valves If you use a Presta valve tube in a rim drilled for Schrader valves, you'll notice that the hole is too big. This isn't a problem unless you ride with low air pressures as some off-ride cyclists like to. In that case, the Presta valve may creep as the tube shifts inside the tire. This can lead to a bent or broken valve over time. To prevent this miscue, install rim grommets, O-ring-like rubber washers that fit in the valve hole reducing its diameter to match the Presta's. 4. Protect The Valve When Pumping An important tip about valves is that they're not indestructible and they're at the most risk when you're pumping up the tire using your frame-mounted pump. To protect the valve, always support it by holding the end of the pump that's on the valve in such a way that you can hook a thumb or finger over the tire. That way, as you push to inflate the tire, you're pushing against your hand and not the valve, which will bend or break if you push against it alone. 5. Valve Nuts A common question with Presta valves is whether or not it's important to install the valve nuts (knurled metal rings that are used with threaded valves). Not all Presta valves are threaded from top to bottom. But, if yours are threaded, there's a good chance that there are valve nuts on them. These can make it easier to inflate the tire because they hold the valve proud of the rim making it easier to get the pump head on them. Be sure not to tighten them too much, however, or they'll be difficult to remove by hand when you have to fix a flat on the road or trail. Overtightening the nut can also put pressure on the valve/tube junction where it passes through the rim and cause a flat. 6. Dealing With Slow Leaks One final tip: when you're searching for a slow leak, don't ignore the valve. Sometimes valves fail and air seeps out. To check, put a little spit on the end of the valve and stare at it for a few seconds. If the valve is leaking, a bubble will form. Often you can tighten the valve and the leaking will cease. If this doesn't do the trick on a Schrader valve, try removing the valve core, putting a drop of oil on the spring and reinstalling the core. This will usually stop the leak. To work on Schrader valves you'll need a valve cap with a built-in valve tool or a separate valve tool. These have pronged ends that fit inside the valve to grip and turn the core. They're available at auto-parts stores.

  • Author:
  • Posted By:







Related Sponsors