Bicycle brake systems

pl:System hamulcowy roweru This article lists the different types of bicycle braking systems.

Early bicycles such as the high wheeled penny-farthing bikes had no brakes as we would recognize them. A rider who wanted to stop had to jump off the bike as it was moving. Unsurprisingly there were many accidents, many of them fatal, which limited the appeal of cycling, mostly to young and adventurous men.

The 1870s saw the development of the "safety bicycle" which was roughly the bicycle we would recognize today, with two wheels of equal size, driven by a chain, with pneumatic tires.

The braking system these bicycles used was often a simple leather pad which pressed against the top of the tire, which was driven by a rod attached to a lever on the handlebar, and there was no rear brake. This was undoubtedly a big improvement on having no brakes at all, but it was not very powerful and had the big drawback that it was almost useless in wet weather.

After that the next big advance in bicycle braking, which came around the 1890s, was the invention of the rim brake. This is the type of brake most commonly used on bicycles today.

Rim brakes

Rim brakes, as has already been mentioned, are the most common type of bicycle brake in use today. Essentially they use two pads (usually made of leather or rubber) to press in a scissor-like fashion against the side of the rims, thus causing friction and slowing or stopping the bike. The power of the braking depends on how hard the pads push against the rims.

This force is applied by the rider squeezing a lever mounted on the handlebar, and transferred to the brake by means of a Bowden cable, or sometimes a rod. There are several different designs of rim brakes. Sidepull caliper brakes are widely used on inexpensive bikes, as well as on high-quality road bikes. These consist of two arms that pivot in the middle. These arms have extensions on one side. The cable housing is attached to one extension, and the inner cable to the other so that when the brake lever is squeezed the calipers move together. These brakes are simple and effective when designed for relatively narrow tires, however they have serious disadvantages when they are big enough to fit wide tires. Most of these disadvantages are answered with some form of cantilever brake.

The larger tires on mountain bicycles presented a braking problem with standard calipers, because the long distance from the pivot to the pad allows the arms to flex, reducing effectiveness. In higher-quality fat tire bikes this was solved by using cantiliver or V brakes that use two seperate pivots on the frame or fork just below the rim.

Cantilevers have pivot points mounted to each side of the frame or fork, usually just below the rim. The traditional cantilever has an L shaped arm on each side, with a straddle cable between the arms. The cable from the brake handle pulls upwards on the straddle cable, causing the brakes to rotate up and inward. These require a cable stop on the frame or fork to hold the cable housing. V brakes (sometimes called direct-pull) mount similarly, but the arms extend straight up, and the outer housing is attached to one arm, the inner housing to the other. Closely related is the U brake. Unlike standard cantilevers, the pivots are above the rim. The arms cross over, and usually have the same type straddle cable as a cantilever. This was used for a short time on mountain bikes, and somewhat longer on BMX bikes. It's main advantage was that it did not protrude from the frame like the early cantilevers. This advantage was reduced by redesigned low-profile cantilevers and nearly eliminated with V brakes.

Some older road bikes used centerpull brakes. This had arms similar to a U brake, but the pivots were mounted to a crosspiece that attached to the same place as calipers, rather than being a part of the frame.

Rod brakes use a series of rods and pivots rather than Bowden cables. They require a special rim with the braking surface inside on either side of the spokes, rather than on the sides. The brakes pull upwards rather than pinching together. Although rod brakes are heavy and in some ways complex, they can be repaired with simple hand tools where replacement Bowden cables are not available or too expensive.

The advantage of rim brakes is that they are cheap, lightweight, mechanically simple and easy to maintain. Also, modern designs of rim brakes are very powerful.

One major disadvantage of rim brakes is that they need regular maintenance. Brake pads wear down frequently due to friction against the rim, and therefore they have to be replaced at regular intervals. Also, if used over long periods of time, rims also wear out due to friction and have to be replaced. Bowden cables can wear or rust.

The other main disadvantage of rim brakes is that their performance deteriorates in wet weather when the rims are wet, although this problem is far less serious on bikes which use rims made of Aluminum alloy. They are also prone to clogging with mud when mountain biking in wet conditions.

Disc brakes

This type of brake is most suitable for and found mainly on mountain bikes which are ridden off road.

Although this type of brake has been used on motorbikes for decades, only recently have they been added to bicycles. A disk brake consists of a metal disk attached to the wheel hub that rotates with the wheel. Attached to the frame or fork will be calipers and pads that squeeze together on the disk.

The main advantage of disc brakes is that their performance is equally good in all conditions including water and mud . They also avoid the problem that rim brakes have of wearing out the wheel rims, especially in muddy conditions.

On some expensive disk brake models, a Hydraulic system is used to push the pad instead of a cable.

On the down side, however, they are usually heavier and more expensive than rim brakes, and in most cases require a special hub.

Hub brakes

Hub brakes are brakes that have their mechanism enclosed within the hub of the wheel, and are usually fitted to the back wheel. They are drum brakes which are the type of brake used on cars. Because they are enclosed, hub brakes are completely unaffected by the weather. Some types of hub brake are operated by cables and levers, in the same way as rim and disk brakes. Other types are operated by the rider turning the pedals backwards, these are known as "back pedaling brakes", or "coaster brakes".

In addition to being impervious to changes in the weather, hub brakes have the advantage of needing very little regular maintenance, especially the back pedaling type.

On the downside, when hub brakes do require maintenance it is far more complicated than other braking systems. They occasionally need to be dismantled and re-greased, usually by a professional. Also hub brakes are heavier than all the other types of bicycle brake. Coaster brakes are not compatible with derailleur gears.

Hub brakes are used mainly on utility bikes, and also on some tandems used in mountains. In the tandem use, the drum is not intended to stop the bike. Instead they are used to keep the speed down on long downhill sections where extended use of rim brakes can cause overheating, which can in turn cause tire damage.

Braking technique

Effective use of a bicycle brake is highly counter-intuitive. Simply put, the most important rule is: use the front brake almost exclusively.

During braking (either with the front or rear brake), most of the cyclist's weight is transferred to the front wheel, leaving the rear wheel with almost no force keeping it pressed against the ground. Thus rear brake, especially in wet conditions or going downhill, can exert little braking force before the wheel locks and starts skidding. A skidding rear wheel can lead to dangerous, uncontrollable bicycle movements eventually resulting in the cyclist falling on the ground.

Also, the rear brake can only produce a fraction of the braking force easily provided by the front brake. In emergencies, it is important to grab the front brake and press it hard to stop in the minimum possible distance.

The casual rider will at first avoid using the front brake, due to the unsettling feeling of "toppling up". It is important to explain the issue and invite the rider to give both brakes a few tries, simulating an emergency situation. In a severe stop, the rider should shift their weight as far to the rear as possible. Theoretically, the fastest stop is accomplished by maintaining enough pressure that the back wheel is barely touching the ground, just before flipping over the handlebars. In the real world this isn not practical--Instead, use light pressure on the back wheel, hard pressure on the front. The back wheel is primarily useful as an indicator-when it starts to skid reduce the pressure to both brakes to prevent flipping over the front wheel, then increase both again.

There are a few special situation where limited use of the front brake, and heavier involvement of the rear brake is advisable: on extremely slippery surfaces, like mud, snow or ice. But this should be considered the exception and not the rule.

External links

• Bicycle Repair: Adjusting brakes (http://wikibooks.org/wiki/Bicycle_Repair_Adjusting_brakes)