Maintenance
Bowden cables can cease to function smoothly, particularly if water or contaminants get into the housing. (Modern lined and stainless steel cables are less prone to these problems; unlined housings should be lubricated with a light machine oil.) Cables also wear through repeated use over a long time, and can be damaged through kinking or raveling. A common failure occurs on bicycles at the point where the housing enters a barrel adjuster; loose housing ends tend to fray the housing, making adjustments uncertain. Fraying due to fatigue is most likely if the cable passes over a pulley, which on bicycles is often below the recommended diameter, or where the cable is bent repeatedly where it attaches to the brake lever or caliper. Sharp bends tend to furrow the inner cable sleeves, though its significance for gear shifting and braking is poorly documented. If an inner cable is not replaced when it frays, it can suddenly break when force is applied strongly, causing the link to fail when most needed (e.g. to a brake).
The specifications for cables and housings rarely give any details other than dimensions and the purpose of the products. The specific resistance to compression or bending is never quoted, so there is much rhetorical evidence and comment as to the performance and durability of products, but little available science for the consumer's use. A particularly severe quality test for housings is at or near the hinge of a folding bicycle where a sharp bend is made repeatedly. The radius of curvature of cables on a folded bicycle can be as low as 1.5 inches, (4 cm.), so it is as well to shift to the gear with the lowest cable pressure before folding, to minimize any adverse effects on housings or derailleurs. This gear is usually the one with the highest index number on the gear shifter.
There is some controversy surrounding the existence of the phenomenon known as "cable stretch". Newly installed cables can seem to elongate, requiring readjustment. While it is generally agreed that inner wires actually stretch very little - if at all - housings and linings may compress slightly, and all parts may generally "settle in". Lightweight assemblies such as those used on bicycles are more susceptible to this phenomenon.
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