Construction, installation and maintenance of various types of brakes.

Construction, installation and maintenance of various types of brakes.

For braking, the next brakes are used.

Rim brakes

  • afbeelding 14Caliper brake. Lightweight brakes, commonly used on road bikes. On other bikes almost not used because they can only be used in combination with narrow tires. (See Figure 14).

 

 

 

 

 

 

 

 

  • afbeelding 15Centre-pull caliper brakes have symmetrical arms and as such centre more effectively. The cable housing attaches to a fixed cable stop attached to the frame, and the inner cable bolts to a sliding piece (called a “braking delta”, “braking triangle”, or “yoke”) or a small pulley, over which runs a straddle cable connecting the two brake arms. Tension on the cable is evenly distributed to the two arms, preventing the brake from taking a “set” to one side or the other.These brakes were reasonably priced, and in the past filled the price niche between the cheaper and the more expensive models of side-pull brakes. (See Figure 15).

 

 

 

 

  • afbeelding 16The cantilever brake is a class of brake in which each arm is attached to a separate pivot point on one side of the seat stay or fork. Thus all cantilever brakes are dual-pivot. Both first- and second-class lever designs exist; second-class is by far the most common. In the second-class lever design, the arm pivots below the rim. The brake shoe is mounted above the pivot and is pressed against the rim as the two arms are drawn together. In the first-class lever design, the arm pivots above the rim. The brake shoe is mounted below the pivot and is pressed against the rim as the two arms are forced apart.Cantilever brakes are preferred for bicycles that use wide tyres, such as those on mountain bikes. (Standard caliper brakes are problematic in these applications since the long distance from the pivot to the pad reduces mechanical advantage and allows the arms to flex, reducing braking effectiveness.) Because the arms move only in their designed arcs, the brake shoe must be adjustable in several planes. Thus cantilever brake shoes are notoriously difficult to adjust. As the brake shoes of a second-class cantilever brake wears, they ride lower on the rim. Eventually, one may go underneath the rim, so that the brake does not function.There are several brake types based on the cantilever brake design: cantilever brakes and direct-pull brakes – both second class lever designs – and roller cam brakes and U-brakes – both first class lever designs. (see figure 16 ).

 

  • afbeelding 18Linear-pull brakes or direct-pull brakes, commonly referred to by Shimano’s trademark V-brakes, are a side-pull version of cantilever brakes and mount on the same frame bosses. However, the arms are longer, with the cable housing attached to one arm and the cable to the other. As the cable pulls against the housing the arms are drawn together. Because the housing enters from vertically above one arm yet force must be transmitted laterally between arms, the flexible housing is extended by a rigid tube with a 90° bend known as the “noodle”. The noodle seats in a stirrup attached to the arm. A flexible bellows often covers the exposed cable.Since there is no intervening mechanism between the cable and the arms, the design is called “direct-pull”. And since the arms move the same distance that the cable moves with regard to its housing, the design is also called “linear-pull”. The term “V-brake” is trademarked by Shimano and represents the most popular implementation of this design.V-brakes function well with the suspension systems found on many mountain bikes because they do not require a separate cable stop on the frame or fork. Because of the higher mechanical advantage of V-brakes, they require brake levers with longer cable travel than levers intended for older types of brakes. Mechanical (i.e. cable-actuated) disc brakes use the same amount of cable travel as V-brakes, except for those that are described as being “road” specific. (See Actuation mechanisms below.) As a general rule, mechanical disc brakes for so-called “flat bar” bicycles (chiefly mountain and hybrid bicycles) are compatible with V-brake levers, whereas mechanical disc brakes intended for “drop-bar” bicycles are compatible with the cable pull of older brake designs (cantilever, caliper, and U-brake).Cheap or poorly-specified V-brakes can suffer from a sudden failure when the noodle end pulls through the metal stirrup, leaving that wheel with no braking power whatsoever. Although the noodle can be regarded as a service item and changed regularly, the hole in the stirrup may enlarge through wear. The stirrup cannot normally be replaced, so good quality V-brakes use a hard and tough steel for the stirrup. (see figure 18).

 

  • afbeelding 19Hydraulic rim brakes are one of the least common types. These brakes are mounted either on the same pivot points used for cantilever and linear-pull brakes or they can be mounted on four-bolt brake mounts found on many trials frames. They were available on some high-end mountain bikes in the US in the early 1990s, but declined in popularity with the rise of disc brakes. The moderate performance advantage (greater power and control) they offer over cable actuated rim brakes is offset by their greater weight and complexity. The only significant current use of these brakes in the US is on bicycles used for trials riding, but in Europe the Magura hydraulic rim brakes are still in use. (see figure 19 and 20).

afbeelding 20

 

 

 

 

 

 

 

 

Hub brakes

  • afbeelding 21A disc brake consists of a metal disc attached to the wheel hub that rotates with the wheel. Calipers are attached to the frame or fork along with pads that squeeze together on the disc. As the pads drag against the disc, the wheel – and thus the bicycle – is slowed as kinetic energy (motion) is transformed into thermal energy (heat). (In basic operation, disc brakes are identical to rim brakes.) A bicycle disc brake may be mechanically actuated, as with a Bowden cable, or hydraulically actuated, or a combination of the two.Disc brakes are used mainly on mountain bikes ridden off-road, but sometimes on hybrid bicycles and touring bicycles. A disc brake is sometimes employed as a drag brake. (see figure 21).

 

 

 

 

  • afbeelding 23First invented in 1898 by Willard M. Farrow, the coaster brake, also known as a back pedal brake or foot brake (torpedo or contra in some countries, in Italy contropedale), is a type of drum brake integrated into the back hub with an internal freewheel. Freewheeling functions as with other systems, but when back pedaled, the brake engages after a fraction of a revolution. The coaster brake can be found in both single-speed and internally geared hubs.When such a hub is pedaled forwards, the sprocket drives a screw which forces a clutch to move along the axle, driving the hub shell or gear assembly. When pedaling is reversed, the screw drives the clutch in the opposite direction, forcing it either between two brake shoes and pressing them against the brake mantle (which is a steel liner within the hub shell), or into a split collar and expanding it against the mantle. The braking surface is often steel, and the braking element brass or phosphor-bronze, as in the Birmingham-made Perry Coaster Hub. Crude coaster brakes also exist, usually on children’s bicycles, where a serrated steel brake cone grips the inside of the hub shell directly, with no separate brake pads or mantle. These offer a less progressive action and are more likely to lock the rear wheel unintentionally.Unlike most drum brakes (but like a Shimano roller brake) a coaster brake is designed to run with all its internal parts coated in grease for quiet operation and smooth engagement. Most grey molybdenum disulphide greases work well in a coaster brake, with its metal-to-metal friction surfaces.

    Coaster-brake bicycles are generally equipped with a single cog and chain wheel and often use ⅛ in (3.2 mm) wide chain. However, there have been several models of coaster brake hubs with dérailleurs, such as the Sachs 2×3. These use special extra-short dérailleurs which can stand up to the forces of being straightened out frequently and do not require an excessive amount of reverse pedal rotation before the brake engages. Coaster brakes have also been incorporated into hub gear designs – for example the AWC and SRC3 from Sturmey-Archer, and the Shimano Nexus 3-speed. They can have up to eight gears, like the Nexus inter-8. (see figure 23).

 

  • afbeelding 22A Roller Brake is a modular cable-operated drum brake manufactured by Shimano for use on specially splined front and rear hubs. Unlike a traditional drum brake, the Roller Brake can be easily removed from the hub. Some models contain a torque-limiting device called a power modulator designed to make it difficult to skid the wheel. In practice this can reduce its effectiveness on bicycles with adult-sized wheels. (see figure 22).

 

 

 

  • afbeelding 24Bicycle drum brakes operate like those of a car, although the bicycle variety use cable rather than hydraulic actuation. Two pads are pressed outward against the braking surface on the inside of the hub shell. Shell inside diameters on a bicycle drum brake are typically 70–120 mm (2.756–4.724 in). Drum brakes have been used on front hubs and hubs with both internal and external freewheels. Both cable- and rod-operated drum brake systems have been widely produced.(see figure 24).

 

 

 

 

 

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