Considering How Cables Control a Bike

Despite the important role of bike cables, they rarely get the respect they deserve. They usually play second fiddle to their sexier companions, the shifters, brake levers, derailleurs, and brakes. The truth is, improperly installed or worn-out cables can prevent even the best derailleurs and brakes from functioning properly. When a squirrel jumps out in front of you while you’re hurtling down a hill on your bike, you’re not only counting on your brakes to grip the wheels and slow you down, but you’re depending on your cables to transfer the force from your clenching grip to the brakes.

Although cables have long been used to transfer force when pulled, bike cables are unique in that they have to transfer force around the curves and corners of a bike. The design of the cable with an inner wire supported by a stiff outer housing made of steel and covered plastic makes this possible.

Most bike cable housings have a liner made of plastic, nylon, or Teflon. This liner sits between the wire and the housing to help reduce friction. In older cables, wires didn’t have such a liner; because they came into contact with the housing, they required grease for lubrication.

In order to save weight and reduce the amount of friction, many bikes are designed to use cables with the inner wire exposed. The cable housing runs along a portion of the frame until it comes to a stop. The cable housing is fed into the narrow opening in the stop, which allows only the inner wire to pass through. To ensure a snug fit in the stop, a small metal cap, called a ferrule,usually covers the end of the housing. From here, the wire continues on until it comes to another stop, facing in the opposite direction, where the cable housing begins again.

Not just any cable housing can be used with a bike. For index gears, you use a different style, higher-quality,non-compressing cable housing. It’s made with separate wires running parallel inside the housing and is held together by plastic.

Higher-quality cable housing for shifting shouldn’t be used for brakes, because it may not be able to handle the higher force applied during severe braking.

Less flexible non-compressing “gear” housing, though more expensive, is a different style and not necessarily higher quality. The only real benefit is that the index adjustment holds better than conventional housing. The failure rate of this housing is significant, and many people use brake housing for derailleurs anyway, although that usually means an additional adjustment to get the indexing correct.