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Overview of Tubes


Bicycle nner tubes have an obviously valuable position on the bike though there have been attempts to find replacements. A few years ago, a product was introduced that replaced the tire and the inner tube with a nearly solid polyurethane tire that didn't use a tube. The polyurethane tire gave up some important ground adhesion characteristics as well as some real shock absorption provided by the tube. But its real failing was when many who bought them from us had their wheels fail altogether. It seems the polyurethane tire transmitted so much road shock into the rim that over time, the spoke nipples began to "back off" and become loosened, leading to catastrophic wheel failure with no apparent notice. We're telling you this story, because all of a bicycle inner tube's functionality isn't obvious.

Inner Tube Sizing For many years the bicycle industry labeled tube boxes with the exact diameter and width of a known tire size, which obligated stores to inventory tubes boxed and labeled for every known tire size, even if the same model of tube was used in several differently labeled boxes. In the 1980's some bike store owners and some importer/distributors became more savvy to the concept that the same tube was being packaged in boxes labeled differently only in the "size" listed on it. Tubes started to come boxed with a size "range" printed on it. The box would state a wheel diameter then give a width "range" that the tube would accommodate. An example would be 26 x 1.95-2.125", this tube is intended to fit a 26" tire whose nominal width is between 1.95" and 2.125". The truth about tube sizing is more simple still. It will work, provided the diameter is at least close, for mountain tires if the width is within 3/4", or for road tires if the width is within 3/8" of the nominal tire size. Remember, the nominal tire width is almost always somewhat bigger than the actual width, and rubber itself is an elastic substance that stretches considerably under pressure without failure. As an example, to take the tire product images (photographs) used in the tire article, we used a 26 x 1.6" tube for all tires that had a nominal width greater than 26 x 1.25. We used a 26 x 1.0" tube for the 26 x 1.1" and 26 x 1.25" tires. The same tube elasticity permits you to use a smaller diameter tube in a nominally larger diameter tire, which is why 700c and 27 " tubes are used interchangeably. In a pinch, if you find yourself with only an obviously larger diameter tube, say a 700c/27" diameter though you need it for a narrow 26" tire, some expert riders will fold the tube back on itself, install it in the tire and inflate it normally (usually without any performance loss). Serious riders as a rule, for weight reduction purposes, will choose the proper diameter tube with the smallest acceptable width for their inner tube.

Air Porosity As we mentioned in our "About Rubber" article, synthetic butyl rubber is the most frequently used choice for tube manufacture. It will contain a volume of "gas", in our case air, for ten times the length of time that latex rubber will. But all rubbers have some "porosity" to air, meaning it leaks out through the rubber itself. Over time even a butyl rubber inner tube will lose its internal air pressure until the inner atmosphere in the tube and the outer atmosphere are equal. To the outward observer, your bike, left unattended, will appear to have two flat tires. In truth, the tube is still functioning correctly, the air under pressure has merely leaked through the tube's wall. If you merely inflate the tubes you'll find they have no real puncture. We can't tell you how many times customers have brought their bikes into our service department to have both tubes replaced and insisted we replace them when we knew it was unnecessary. And, at our end it's uncomfortable, but we sometimes find ourselves replacing good tubes at the customer's insistence though we know it may not be needed, just to preserve the customer's state of mind. After an absence from riding your bike first re-inflate its tubes to detect if there is really a puncture.

Tire/Tube Installation Tools Both Kevlar and steel wire bead tires fit snugly on the rim, some more snugly than others, because you don't want the tire to blow off the rim under pressure in use. This desirable snugness however leads to consternation when you have to remove the tire. Generally you have to pry a part of one of the tire beads off the rim so you can remove one side of the tire from the rim. Unfortunately many people use something other than "tire levers" to pry the tire off. Sometimes a flat bladed screwdriver is used, other times it may be kitchen implements, notably spoons, to pry the tire off and then back on again with the new tube inside. When using a metal object to pry the tire on or off (with the tube partially inflated during installation ), the tube frequently becomes caught between the metal pry device and the metal rim, and you actually puncture the new or patched tube by pinching it between these metal surfaces. We recommend using nylon plastic prying implements so this doesn't happen. Tire levers have a tapered thickness, with a concave end that slides under the tire bead and uses the rim edge as a fulcrum to lift it over the rim. The opposite end of the lever generally has a hook that permits you to hook it on a spoke, holding that pried tire off the rim while you use a second or third lever nearby on the tire to free enough from the rim that the tire side comes free of the rim. Done properly, after removing one side of the tire, you then pull the tube out of the tire and grip the tire just pull it up and over the rim using just your hands (with no tools needed for the second side). In many instances wide 26" mountain tires can be removed and installed using your hands alone. Once you become slightly accomplished, installation can be performed with no pry tools for all tires (except in a few cases of largely French tires).





New Tube Inflation Everyone is always justifiably in hurry. Many times a tire and wheel with a newly installed tube is inflated for the first time by an air compressor. Air compressors force air so quickly into a new tube and tire that the tire's bead doesn't have enough time to settle and "seat" within the rims' inner bead "hook". If the tire bead doesn't seat properly, as the tube is inflated, it may force a small section off the rim again, and the tube will inflate between the rim and the off the rim tire section. This bulging area of the tube outside the tire will burst producing an un-patchable star shaped hole and you will have to replace the tube again. To avoid this whole unseating and bursting process (which takes just a couple of seconds with a compressor) we recommend that the first time you inflate a newly installed tube, you use a hand pump. When you use a hand pump, the tire will slowly shift on the rim and then seat, without the tire blowing off the rim. Still, when using a hand pump, it is wise to look at the tire during inflation to see that it stays on the rim, and that the exposed area of the tire chafing strip is equal around the circumference of the tire when you are finished. If the chafing strip exposure varies greatly around the tire it will produce a "flat spot" on the inflated tire, and will create an uncomfortable thumping noise and a "bump" in feel while you ride on it. If a flat spot develops or the tire becomes unseated while inflating it, release the air immediately, correct the mistake and re-inflate by hand again until you are successful.

Valve Types There have been three types of air valves used used for bicycles in the last 50 years. They are the Dunlop, Schraeder, and Presta valves.

The Schraeder valve, also known as the "standard" or "American", is most frequently used in the United States. This is also the type of valve used on automobile tires. The valve stem is covered leaving 9mm of exposed brass threads for the valve cap to screw ontoÄ. Inside the valve is a removable "core" that uses a spring assembly to force the valve shut. When you push a small steel pin in the center of the valve, you compress the spring and the valve is "opened". The Schraeder core is removed with a core removal tool or a "split top " valve cap. It has a horizontal cut making two prongs that loosen up the valve core "seat". Presta valves are also known as "French" valves. Because it's slightly lighter than the Schraeder valve they have been used on European bicycle tubes for many years, and have always been used in "high performance" bicycle applications, chiefly sew-up or tubular tires and ultimately for clincher tires. The entire length of the exposed brass Presta valve stem is threaded, and a Presta tube generally comes with a round "nut". When the tube has been properly installed and inflated, this outer nut is screwed down the valve stem to hold the valve in place, so it doesn't shift and then shear off from the tube.

The Presta valve has no internal spring to keep it closed, instead it relies on the inflated internal pressure being higher than the outer atmosphere. When the inner pressure is higher it forces the valve shut, then a small brass nut on its non-removable core is tightened clockwise, holding the valve "closed" until the core nut is loosened and downward pressure is applied on the core piece releasing the air.

The Dunlop valve is a variation on the Schraeder valve, but hasn't been seen or used commonly for several years. Unlike the other two types, it wasn't molded into the tube at manufacture and could be taken from a spent tube and installed in another tube. The exterior of the Dunlop valve was threaded for an air tight nut that held the valve assembly in place through a hole in the tube. The valve core and air release of the Dunlop valve was the same as that of the Schraeder valve.

"Seamless" is a term to describe some tubes that are usually molded of butyl rubber. At one time all tubes were made of latex rubber using a length of rubber tubing, with one of the ends fitted into the other, then cemented or vulcanized together. The area where the ends were fit into each other created a small area of overlap in the thickness of the rubber is referred to as a "seam". In some instances where a very thin tire is used, this overlap adds thickness that may cause a slight rise in the tire, making it ever so slightly out of perfect round. To minimize this overlap effect, the seam is positioned where the valve passes through the tube, and actually adds some reinforcement to the valve area. All the latex tubes we sell have a seam, and that seam occurs under the valve.

Butyl or Latex? - As we've mentioned before, butyl rubber is the industry's choice for common replacement inner tubes, though we do sell some tubes made wholly or chiefly from latex rubber. The latex tubes are far more expensive because latex sap, its basic raw material, is labor intensive to extract. The benefits of using latex inner tubes are the slightly enhanced handling characteristics. Because the latex rubber a little more supple, it adapts quickly to a tire's changed shape while cornering or rolling over small obstacles. Latex tubes generally have a thinner rubber wall that adds to its lightweight reputation, but latex rubber doesn't hold air as long as butyl rubber because it is more gas permeable and gas porous, so the latex tube must to be inflated more frequently. The butyl rubber compound retains most of latex rubber's suppleness and moves pliantly as the tires' shape changes. It adds its low gas permeability so it holds air at pressure longer and is much cheaper than latex.



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