Bicycle brake systems

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Bicycle brake systems

Post  Jivko on Sun Jun 06, 2010 2:52 am



I really enjoy cycling.I have a bike too and I want to share little information about brakes and stuff I found on the Internet. Smile

Lets begin. Very Happy

Bicycle brake systems are used to slow down or stop a bicycle. There have been various types of brakes used throughout history, and several are still in use today. The three main types are: rim brakes, disc brakes, and drum brakes.

Rim brakes

Rim brakes are so called because braking force is applied by friction pads to the rim of the rotating wheel, thus slowing it and the bicycle. Brake pads can be made of leather or rubber and are mounted in metal "shoes". Rim brakes are typically activated by the rider squeezing a lever mounted on the handlebar.

Advantages and disadvantages

Rim brakes are cheap, light, mechanically simple, easy to maintain, and powerful. However, they perform poorly when the rims are wet. This problem is less serious with rims made of aluminum, than on those with steel or chromed rims. Rim brakes are also prone to clogging with mud, particularly when mountain biking.

Rim brakes require regular maintenance. Brake pads wear down and have to be replaced. Over longer time and use, rims become worn. Rims should be checked for wear periodically as they can fail catastrophically if the braking surface becomes too worn. Wear is accelerated by wet and muddy conditions. Some type of rim brakes e.g. dual pivot, require that the rim be relatively straight; if the rim has a pronounced wobble, then either the brake pads rub against it when the brakes are released, or apply insufficient or uneven pressure to the rim.

Rim brakes also heat the rim because the brake functions by converting kinetic energy into thermal energy. In normal use this is not a problem, as the brakes are applied with limited force and for a short time, so the heat quickly dissipates to the surrounding air. However, on a heavily-laden bike on a long descent, heat energy is added more quickly than it can dissipate and temperature at the rim and its enclosed tube can increase tyre pressure so much that the tyre blows off the rim. If this happens on the front wheel, a serious accident is almost inevitable. The risk can be reduced by using both brakes,or by fitting a drag brake.

Although becoming superseded by disc brakes on off-road machines, rims with a hard, rough ceramic coating on the braking surface are available. This coating significantly reduces rim wear and can also improve both wet and dry braking provided appropriate pads are used. It also reduces heat transfer to the air in the tyre because the ceramic coating, although thin, is a thermal insulator.[citation needed]

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.) Cables also wear through repeated use over a long time, and can be damaged through kinking or raveling. Fraying due to fatigue is most likely if the cable passes over a pulley, which on bicycles is often below the recommended diameter,[4] or where the cable is bent repeatedly where it attaches to the brake lever or calliper. If an inner cable is not replaced when it frays, it can suddenly break when the brake is applied strongly, causing the brake to fail when most needed.

Disc brakes



A disc brake consists of a metal disc attached to the wheel hub that rotates with the wheel. Callipers 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.

Advantages and disadvantages

Disc brakes tend to perform equally well in all conditions including water, mud, and snow due to a several factors:

* The braking surface is farther from the ground and possible contaminants like mud which can coat or freeze on the rim.
* Disc brake pads when fully retracted ride much closer to the braking surface than rim brake pads.[20] This better prevents a buildup of water or debris under the pad.
* There are holes in the rotor, providing a path for water and debris to get out from under the pads.
* Wheel rims tend to be made of lightweight metal. Brake discs and pads are harder and can accept higher maximum loads.


Disc brakes offer better modulation of braking power and generally require less effort at the lever to achieve the same braking power.[citation needed]

The use of very wide tyres favors disc brakes, as rim brakes require ever-longer arms to clear the wider tyre. Longer arms tend to flex more, degrading braking. Disc brakes are unaffected by tyre width.

Disc brake assemblies are generally more expensive than rim brakes.

Disc brake assemblies are often heavier than rim brakes. Disc brakes require a hub built to accept the disc and a bicycle frame or fork built to accept the calliper. A disc brake puts more stress on a wheel's flanges, spokes, nipples, and rim spoke bed than a rim brake, since the torque of braking is between the hub and the rim.[citation needed] This leads to heavier and more expensive wheels. Forks made to handle the forces of a front disc brake are heavier than those for rim brakes and may have different ride qualities.

Front hubs designed for discs often move the left hub's flange inward to make room for the disc, which causes the wheel to be dished. A dished wheel is laterally weaker when forced to the non-disc side. Other hubs use conventional flange spacing and provide a wheel without dish, but require a less common wide-spaced fork.

Disc brakes are sensitive to lateral play or "slop", so careful manufacture and adjustment is required. Hub bearing wear is an issue with disc brakes.

Disc brakes have less of a requirement that the braking surface be straight than do many types of rim brakes. The wheel rim does not have to be true for disc brakes to work, as they do not use the wheel rim to slow the bicycle.

While both types of brakes will wear out the braking surface, especially in muddy conditions, a brake disc is much easier and cheaper to replace than a wheel rim.

Hydraulic brakes rarely fail, but failure tends to be complete, whereas mechanical brakes rarely fail completely. Hydraulic systems are difficult to repair on the trail, since they require specialized equipment. Both types require maintenance.

While a disc brake does not heat the rim, excessive heat build up can lead to failure. If brake friction exceeds convection and radiation losses, the temperature of the disc can quickly rise to where the metal weakens, causing the disc to warp or crack. Further, hydraulic fluid may boil from excessive heat. This causes complete brake failure as the brake loses its ability to transmit force ("brake fade") through incompressible fluids, since some of that fluid has become a compressible gas.

The design and positioning of disc brakes can interfere with pannier racks not designed for them. For this reason, many manufacturers produce "disc" and "non-disc" versions.

Since about 2003, riders have reported a dangerous problem using disc brakes. Under hard braking, the front wheel has come out from the dropouts. The problem occurs where the brake pads and dropouts are aligned so the brake reaction force tends to eject the wheel from the dropout. Under repeated hard braking, the axle moves in the dropout in a way that unscrews the quick release. Riders should make sure the skewers are properly tightened before riding. Forks that use different brake/dropout orientations or through axles are not subject to this problem.

Drum brakes



Main article: Drum brake
Shimano Roller Brake unit on an internally geared hub.

Bicycle drum brakes operate like those of a car, although the bicycle variety use mechanical 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. 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.

A roller brake is a modular cable-operated drum brake for use on specially splined front and rear hubs. Unlike a traditional drum brake, the Roller Brake can be easily removed from the hub. It also contains 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.
[edit] Advantages and disadvantages

Drum brakes are useful for wet or dirty conditions since the braking mechanism is fully enclosed. They are heavier, more complicated, and often weaker than rim brakes, but require less maintenance. They are most common on utility bicycles in some countries, especially the Netherlands, and are also often found on freight bicycles and velomobiles.

Source Wikipedia.I hope this info will help you get more experience with brakes and which type is better.

My bike is equipped with rim brakes.Like written in the info they are not useful under wet conditions and they overhead fast when I'm in the mountains and tough terrains.I might change to discs one day.

Anyway be careful while riding. Cool
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Jivko
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Re: Bicycle brake systems

Post  mrsport on Wed Jun 09, 2010 3:14 am

Very useful information.Can you post something about the frames and maybe something about the best producers?Thanks in advance Razz Cool
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