Motorcycle braking systems
Motorcycle braking systems have varied throughout time, as motorcycles evolved from bicycles with an engine attached, to the 220 mph (350 km/h) prototype motorcycles seen racing in MotoGP. Most systems work by converting kinetic energy into thermal energy (heat) by friction. On motorcycles, approximately 70% of the braking effort is performed by the front brake. This however can vary for individual motorcycles; longer-wheelbase types having more weight biased rearward, such as cruisers and tourers, can have a`greater effort applied by the rear brake. In contrast, sports bikes with a shorter wheelbase and more vertical fork geometry can tolerate higher front braking loads. For these reasons, motorcycles tend to have a vastly more powerful front brake compared to the rear.
- 1 History
- 2 Drum brakes
- 3 Disc brakes
- 4 References
- 5 History
- 6 Carbon carbon disc brakes
- 7 Alternative new systems
- 8 References
Early motorcycles which were essentially a bicycle with a motor attached and did not have any braking system beyond slowing the motorcycle down and putting a foot out. One of the first motorcycles to have any sort of braking mechanism was made by Steffey Motorcycles of Philadelphia in 1902. This used a spoon brake operating on the front wheel only. Around 1909 band brakes were introduced, these used a band contracting round the outside of a drum.:16
Douglas motorcycles were available with Research Association disc brakes front and rear on their 1923 RA model, sometimes called TT model, with Freddie Dixon's 1923 sidecar TT-winning machine of that type also having a passenger-operated disc brake for the sidecar wheel.
Drum brakes first started to be fitted to motorcycles in the 1920s and the basic design continues to be used to this day. Originally used for braking both the front and rear wheels, drum brakes have largely been superseded by disc brakes or are used for rear-braking only.:17
The Lambretta TV125 Series 3 was the first modern two-wheeled production machine to be fitted with a disc brake. MV Agusta followed with their limited production 600 cc touring motorcycle announced in 1965:80 which had a pair of cable-actuated Campagnolo front disc brakes.:80 In 1969 Honda released the world's first mass-produced bike to have a disc brake. The CB750 had a hydraulically operated single piston sliding caliper with a solid front disc.:80
In 1989 BMW released the first motorcycle to be equipped with anti-lock brakes (ABS). The system fitted to the BMW K100 LT weighed significantly more than the light weight systems fitted to modern motorcycles.
Drum brakes have a self servo effect. The most common design is a leading-tailing design. More exotic design had four, eight or sixteen shoes. Some motorcycles used finned and/or vented housings for additional cooling, the first of which was AJS.
Hydraulic and mechanical actuation.
Torque reaction arm transfer the torque from the brake to fixed point to relieve the suspension reacting to the braking force i.e. diving
Early cast wheels were not easily compatible with drum brakes.
Sintered pads offer improved heat up time and better wet weather performance. Asbestos was used in the brake pads but its use declined when the negative health impact was discovered.
Brake feel, rotor size.
Combined brake systems
ABS BMW main article
The front suspension on the Yamaha GTS1000 released in 1993 was a single sided swingarm that amongst other characteristics aimed to reduce diving under braking. The design only allowed for a single front disc brake so a comparatively large 330mm disc was mated to a six-piston caliper, a world first on a production bike.:28
Radial master cylinders.
Brake levers, hole in for aerodynamics on race bikes.
Braided brake hoses.
Floating discs have better disc centering with a fixed caliper. A floating disc also avoids disc warping and reduces heat transfer to the wheel hub. Lambretta were the first manufacturer to use floating discs on a volume production motorcycle.
Wavy discs place the mass closer to the axle for reduced inertia, better heat dissipation and lower weight. They were originally developed for Motorcross bikes however they have since seen use on road going motorcycles as well.
Sliding versus fixed
Single action calipers have brake pistons that operate on one side only. This type has a floating pin design which allows the piston side of the caliper to push onto the disc surface and pull the other side into contact as well.:100 Dual action, or opposed calipers, are fixed into position to reduce flex. Dual action have opposed pistons either side of the disc to greatly improve the piston area.
Multi piston calipers
Larger rotors can be used to increase braking force, but this also increases weight and inertia. To overcome this brake manufacturers developed calipers four, six and even eight pistons. Increasing the number of pistons increases the swept piston area, allowing for longer, narrower brake pads and smaller discs.
Caliper mounting techniques
Early disc brake calipers were located in front of the fork leg on top of the disc. This position placed the caliper in an area of high air flow for better heat removal. Calipers on most modern motorcycles are mounted to the rear of the fork leg. This has the advantage of reducing the angular momentum of the fork assembly and improving low speed handling.
A Radial brake caliper is a brake caliper that is radially mounted(parallel to the forward direction) on the braking system. It is more rigid than the traditional axially mounted brake calipers and is commonly used on performance oriented motorcycles. This is due to the fact that unlike axial brake calipers, the radially mounted brakes are not prone to torsional flexing. The lack of slight lateral movement allows more precise braking and crispier feeling brakes.
Another advantage of radial brake caliper is that larger brake rotors can be fitted on existing mounting bracket by increasing the space. It is easier than axial brakes as new mounting brackets are not needed.
On the introduction of slick tires, old axial disc brakes were unreliable and prone to breaking, therefore radial brakes were introduced to motorcycles from Formula One racing.
On the introduction of slick tires, old axial disc brakes were unreliable and prone to braking, therefore radial brakes were introduced to motorcycles from Formula One racing.
In a bid to improve wet weather braking performance, Honda fitted inboard ventilated disc brakes to models such as the VF400F and CBX550F. This saw the front brake assembly enclosed in a vented aluminium hub. The caliper was mounted onto the hub and gripped the disc from the outside. The purpose of inboard discs was to keep the brake assembly dry and allowed the use of cast iron ventilated discs because the shrouding covered any unsightly surface rust on the disc. The system would prove to be short lived with all successive models reverting to the standard uncovered layout thereafter.
Traditionally opposing piston brake calipers are made in two halves which are then bolted together. The advantages of this method are ease and the speed of which the pieces can be made. The disadvantage is that they are less resistant to flex under load. Calipers machined from a single piece of metal are stronger, but much more expensive to make so some manufacturers such as Sumitomo cast the caliper body as one piece and then machine the piston bores externally with the holes created plugged after assembly. This type of caliper design has been used extensively by Yamaha on a wide range of models from its flagship Yamaha YZF-R1 to the more budget Yamaha FZS600 Fazer. Monobloc Brembo first used on the Ducati 1098.
Buell Motorcycle Company introduced a rim-mounted "zero torsional load" disc brake that was claimed to reduce unsprung weight in the wheel-brake system, including lighter wheel spokes that carried no braking load. This style is generically termed a "perimeter brake" for its point of attachment to the wheel, and had been used in smaller numbers by other manufacturers before Buell. They can rarely be found on custom motorcycle spoked wheels.
Carbon carbon disc brakes
Carbon carbon brakes are used in Moto GP. The friction between the carbon discs and carbon pads produces vast amounts of braking force; far greater braking force than conventional steel disc set-ups. They operate have very high operating temperatures, typically between 400-1000 °C. Continuous late braking can overheat carbon carbon brakes as they oxidize and wear out faster. The high temperatures needed for carbon carbon brakes to be effective means that they cannot be used in the wet. For wet races the riders have to switch a conventional steel brake set-up. Aluminium lithium alloy, banned for 2015 season
Alternative new systems
Drag-racing motorcycles can reach speeds up to 256 mph (412 km/h) over the course of the 1⁄4 mile (400 m) race and can use disc brakes in conjunction with parachutes to slow them after the timed run. The Streamliner class of motorcycle land speed record machines are mandated to have parachutes fitted if the motorcycle is capable of exceeding 250 miles per hour (400 km/h).:38
KTM secretly raced a machine with a KERS style regenerative braking system during the 2008 Valenican 125 cc Grand Prix. Although deemed in contravention of the rules, the use of a KERS system preceded its use in Formula 1.
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