The working principle of the bicycle brake cable

Date: 2021.08.16 Viewed:

Take the front of mountain bike brake cable as an example, and explain the principle of the bicycle brake cable intuitively. The basic principle is to pull and push. Pulling is mainly applied on the wire. The wire is pulled through the brake handle, and then the wire pulls the brake pads. The brake pads rub against the brake disc or the rim to generate friction to brake. Push is mainly used in hydraulic disc brakes. By pulling the brake handle, a pump in the handle pushes the oil in the bicycle brake cable pipe, and then the oil pushes the brake pads, and the brake pads perform friction braking. Oil brakes feel good. The disadvantage is that they are expensive and troublesome to repair. The line brakes are cheap and easy to repair. The disadvantage is that they feel bad, and they are easy to rust and difficult to pull over time.

Obviously, if the two brake pads of the brake can be closely attached to the rim of the wheel, the braking effect can be achieved. When we hold the brake lever, we drive the bicycle brake cable to move in the direction of the brake lever, and the left half of the brake is pulled by the bicycle brake cable to move towards the steel rim. This is very intuitive, and there is no need to say more. The puzzle is how is the right half of the brake pushed toward the steel rim?

To understand this problem, you must first understand the structure of the brake cable/tube. The two ends of the brake cable are respectively fixed at the brake lever and the brake cable binding point in the mountain bike. The cable tube wraps the brake cable and can slide freely along the brake cable. The line tube has two layers, the inner layer is made of steel, and the outer layer is rubber. Both the brake cable and the wire tube can be bent to a limited extent (cannot bend arbitrarily like wool), but the length is fixed (ignoring the slight change), and it can neither be stretched nor compressed. The lower end of the line tube is connected to a steel L-shaped tube, which cannot be bent.

When holding the brake lever, the brake cable moves toward the brake lever. Because the lower end of the bicycle brake cable is fixed, the brake cable has a tendency to be straightened, and the cable tube that is sleeved on the outside of it also has a tendency to straighten. Development, so the line tube begins to stretch, and because the upper end of the line tube will eventually be resisted by a certain part of the brake lever, so the lower end has to be stretched toward the binding point of the brake line, which pushes the L-shaped tube, the L-shaped tube Pushed the left half of the brake closer to the steel ring.

Although the bicycle brake cable and tube look soft, the tube is rigid and incompressible in the longitudinal direction. It is made of steel and the wall is very thick. It is useless to replace it with a rubber tube. Compared with the movement distance of the brake lever, the deformed length of the last one meter of steel wire is negligible, so it can be approximately regarded as rigid. Therefore, the displacement between the wire on the left and the tube can be lossless. Almost is transferred to the right side, and the process will not cause any loss due to the bending degree of the tube/wire or the state of motion.