Disc brakes are generally recognised as the most effective and reliable brakes available for bikes. So far unknown on road bikes, where weight and aerodynamics are most significant, they have become virtually universal on high-end mountain bikes and increasingly common in the middle ground too. They are also becoming common on bikes intended for urban use - city streets are one place where your life might depend on being able to stop quickly!
Not all disc brakes are alike. There are two main types, mechanical and hydraulic.
Mechanical disc brakes (sometimes called cable disc brakes) work on the same principle as rim brakes, except that the pads bear on a disc or rotor rather than on the wheel rim. They are relatively cheap, though still more expensive than a simple rim brake. Because cables are prone to stretch they require relatively frequent adjustment to keep them working effectively.
Hydraulic disc brakes, on the other hand, transmit braking force from lever to brake using a hydraulic fluid, which resists compression. The system is (or should be) completely sealed, which means it requires adjustment much more rarely. However, maintenance does require more specialised tools, and if problems do arise out in the wilds they can be impossible to fix.This is a rare occurrence, usually due to crash damage, but it’s a factor to be considered by anyone planning long wilderness rides.
While hydraulic systems normally require infrequent maintenance, they should still be checked regularly. Brake pads have a long life but do wear out eventually, and it is possible for air bubbles to enter the system. If this happens it is necessary to bleed it and possibly top up the fluid.
Jumat, 18 Juni 2010
History of Disc brakes
Disc-style brakes development and use began in England in the 1890s. The first caliper-type automobile disc brake was patented by Frederick William Lanchester in his Birmingham, UK factory in 1902 and used successfully on Lanchester cars. However, the limited choice of metals in this period, meant that he had to use copper as the braking medium acting on the disc. The poor state of the roads at this time, no more than dusty, rough tracks, meant that the copper wore quickly making the disc brake system non-viable (as recorded in The Lanchester Legacy). It took another half century for his innovation to be widely adopted.
Modern-style disc brakes first appeared on the low-volume Crosley Hotshot in 1949, although they had to be discontinued in 1950 due to design problems. Chrysler's Imperial also offered a type of disc brake from 1949 through 1953, though in this instance they were enclosed with dual internal-expanding, full-circle pressure plates. Reliable modern disc brakes were developed in the UK by Dunlop and first appeared in 1953 on the Jaguar C-Type racing car. The Citroën DS of 1955, with powered inboard front disc brakes, and the 1956 Triumph TR3 were the first European production cars to feature modern disc brakes. The first production car to feature disc brakes at all 4 corners was the Austin-Healey 100S in 1954. The first British company to market a production saloon fitted with disc brakes to all four wheels was Jensen Motors Ltd with the introduction of a Deluxe version of the Jensen 541 with Dunlop disc brakes. The next American production cars to be fitted with disc brakes were the 1963 Studebaker Avanti optional on other Studebaker models, standard equipment on the 1965 Rambler Marlin optional on other AMC models, and the 1965 Chevrolet Corvette Stingray C2. The 1965 Ford Thunderbird came with front disc brakes as standard equipment.
Disc brakes offer better stopping performance than comparable drum brakes, including resistance to "brake fade" caused by the overheating of brake components, and are able to recover quickly from immersion wet brakes are less effective. Unlike a drum brake, the disc brake has no self-servo effect and the braking force is always proportional to the pressure placed on the braking pedal or lever.
Many early implementations for automobiles located the brakes on the inboard side of the driveshaft, near the differential, but most brakes today are located inside the road wheels. An inboard location reduces the unsprung weight and eliminates a source of heat transfer to the tires.
Disc brakes were most popular on sports cars when they were first introduced, since these vehicles are more demanding about brake performance. Discs have now become the more common form in most passenger vehicles, although many particularly light weight vehicles use drum brakes on the rear wheels to keep costs and weight down as well as to simplify the provisions for a parking brake. As the front brakes perform most of the braking effort, this can be a reasonable compromise.
Modern-style disc brakes first appeared on the low-volume Crosley Hotshot in 1949, although they had to be discontinued in 1950 due to design problems. Chrysler's Imperial also offered a type of disc brake from 1949 through 1953, though in this instance they were enclosed with dual internal-expanding, full-circle pressure plates. Reliable modern disc brakes were developed in the UK by Dunlop and first appeared in 1953 on the Jaguar C-Type racing car. The Citroën DS of 1955, with powered inboard front disc brakes, and the 1956 Triumph TR3 were the first European production cars to feature modern disc brakes. The first production car to feature disc brakes at all 4 corners was the Austin-Healey 100S in 1954. The first British company to market a production saloon fitted with disc brakes to all four wheels was Jensen Motors Ltd with the introduction of a Deluxe version of the Jensen 541 with Dunlop disc brakes. The next American production cars to be fitted with disc brakes were the 1963 Studebaker Avanti optional on other Studebaker models, standard equipment on the 1965 Rambler Marlin optional on other AMC models, and the 1965 Chevrolet Corvette Stingray C2. The 1965 Ford Thunderbird came with front disc brakes as standard equipment.
Disc brakes offer better stopping performance than comparable drum brakes, including resistance to "brake fade" caused by the overheating of brake components, and are able to recover quickly from immersion wet brakes are less effective. Unlike a drum brake, the disc brake has no self-servo effect and the braking force is always proportional to the pressure placed on the braking pedal or lever.
Many early implementations for automobiles located the brakes on the inboard side of the driveshaft, near the differential, but most brakes today are located inside the road wheels. An inboard location reduces the unsprung weight and eliminates a source of heat transfer to the tires.
Disc brakes were most popular on sports cars when they were first introduced, since these vehicles are more demanding about brake performance. Discs have now become the more common form in most passenger vehicles, although many particularly light weight vehicles use drum brakes on the rear wheels to keep costs and weight down as well as to simplify the provisions for a parking brake. As the front brakes perform most of the braking effort, this can be a reasonable compromise.
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