Motorcycle components and systems for a motorcycle are engineered, manufactured, and assembled in order to produce motorcycle models with the desired performance, aesthetics, and cost. The key components of modern motorcycles are presented below.
The frame is typically made from welded aluminium or steel (or alloy) struts, with the rear suspension being an integral component in the design. Carbon fibre, titanium and magnesium are used in a few very expensive custom frames.
The frame includes the head tube that holds the front fork and allows it to pivot. Some motorcycles include the engine as a load-bearing stressed member; this has been used all through motorcycle history but is now becoming more common.
Oil-in-Frame (OIF) chassis, where the lubricating oil is stored in the frame of the motorcycle, was used for Vincent motorcycles of the 1950s, and for a while during the 1970s on some NVT British motorcycles. It was widely unpopular and generally regarded as a bad idea at the time. Today it is a used on some "thumpers" (single-cylinder four-strokes) that usually have dry-sump lubrication requiring an external oil tank. It has since gained some cachet in the modern custom bike world too because of the space savings it can afford and the reference to an earlier era.
Modern designs have the two wheels of a motorcycle connected to the chassis by a suspension arrangement, however 'chopper' style motorcycles often elect to forgo rear suspension, using a rigid frame.
The front suspension is usually built into the front fork and may consist of telescoping tubes called fork tubes which contain the suspension inside or some multibar linkage that incorporate the suspension externally.
The rear suspension supports the swingarm, which is attached via the swingarm pivot bolt to the frame and holds the axle of the rear wheel. The rear suspension can consist of several shock arrangements:
- Dual shocks, which are placed at the far ends of the swingarm
- Traditional monoshock, which is placed at the front of the swingarm, above the swingarm pivot bolt
- Softail style suspension, where the shock absorbers are mounted horizontally in front of the swingarm, below the swingarm pivot bolt and operate in extension.
A motorcycle fork is the portion of a motorcycle that holds the front wheel and allows one to steer. For handling, the front fork is the most critical part of a motorcycle. The combination of rake and trail determines how stable the motorcycle is.
A fork generally consists of two fork tubes (sometimes also referred to as forks), which hold the front wheel axle, and a triple tree, which connects the fork tubes and the handlebars to the frame with a pivot that allows for steering.
Almost all commercially available motorcycles are driven by conventional gasoline internal combustion engines, but some small scooter-type models use an electric motor, and a very small number of diesel models exist (e.g., the USMC M1030 M1 version of the Kawasaki KLR650 and the Dutch-produced Track T-800CDI).
The displacement is defined as the total volume of air/fuel mixture an engine can draw in during one complete engine cycle. In a piston engine, this is the volume that is swept as the pistons are moved from top dead centre to bottom dead centre. To the layperson this is the "size" of the engine. Motorcycle engines range from less than 50 cc (cubic centimetres), commonly found in many small scooters, to 5735 cc, a Chevrolet V8 engine, currently used by Boss Hoss in its cruiser style motorcycle.
Motorcycles have mostly, but not exclusively, been produced with one to four cylinders, and designers have tried virtually every imaginable layout. The most common engine configurations today are the single and twin, the V-twin, the opposed twin (or boxer), and the in-line triple and in-line four. A number of others designs have reached mass production, including the V-4, the flat 6-cylinder, the flat 4-cylinder, the in-line 6-cylinder, and the Wankel engine. Exotic engines, such as a radial piston engine, sometimes appear in custom built motorcycles, though two firms Megola and Redrup put radial-engined motorcycles into production.
Engines with more cylinders for the same displacement feel smoother to ride. Engines with fewer cylinders are cheaper, lighter, and easier to maintain. Liquid-cooled motorcycles have a radiator which is the primary way their heat is dispersed. Coolant or oil is constantly circulated between this radiator and the cylinder when the engine is running. Air-cooled motorcycles rely on air blowing past fins on the engine case to disperse heat. Liquid-cooled motorcycles have the potential for greater power at a given displacement, tighter tolerances, and longer operating life, whereas air-cooled motorcycles are potentially cheaper to purchase, less mechanically complex and lighter weight.
An air-cooled engine contracts and expands with its wider temperature range, requiring looser tolerances, and giving shorter engine life. The temperature range of an air-cooled two-stroke is even more extreme and component life even shorter than in an air-cooled four-stroke.
As applied to motorcycles, two-stroke engines have some advantages over equivalent four-strokes: they are lighter, mechanically much simpler, and produce more power when operating at their best. But four-stroke engines are cleaner, more reliable, and deliver power over a much broader range of engine speeds. In developed countries, two-stroke road-bikes are rare, because—in addition to the reasons above—modifying them to meet contemporary emissions standards is prohibitively expensive. Almost all modern two-strokes are single-cylinder, liquid-cooled, and under 600 cc.
In November 2006, the Dutch company E.V.A. Products BV Holland announced that its diesel-powered motorcycle, the Track T-800CDI, achieved production status. The Track T-800CDI uses an 800 cc three-cylinder Daimler Chrysler diesel engine. Other manufacturers, including Royal Enfield, had been producing diesel-powered bikes since at least the 1980s. Also, Intelligent Energy, a British alternative-fuel company, is developing a motorcycle powered by a detachable hydrogen-powered fuel cell, which it calls an Emissions Neutral Vehicle (ENV). According to reports, the vehicle can sustain speeds of 50 mph (80 km/h) while making virtually no noise, and can run for up to four hours without refueling.
Most modern motorcycles have a sequential manual transmission shifted by a foot lever. Some motorcycles, and many scooters, use a continuously variable transmission. Other types of automatic transmission and semi-automatic transmission are also in use.
Engine power can be engaged or interrupted through the clutch, typically an arrangement of plates stacked in alternating fashion, one geared on the inside to the engine and the next geared on the outside to the transmission input shaft.
Power transfer from the gearbox to the rear wheel is accomplished by different methods.
Chain drive uses sprockets and a roller chain, which requires both lubrication and adjustment for elongation (stretch) that occurs through wear. The lubricant is subject to being thrown off the fast-moving chain and results in grime and dirt build up. Chains do deteriorate, and excessive wear on the front and rear sprockets can be dangerous. In a chain drive the power is transmitted into the rear wheel via a cush drive. Conventional roller chain drives suffer the potential for vibration, as the effective radius of action in a chain and sprocket combination constantly changes during revolution ("chordal action"). If a drive sprocket rotates at constant RPM, then the chain (and the driven sprocket) must accelerate and decelerate constantly. Most chain-driven motorcycles are fitted with a rubber bushed rear wheel hub to eliminate this vibration issue.
Small budget motorcycles may have a totally enclosed drive chain, but this is rare on larger motorcycles, an exception being the Norton rotary bikes. To prevent rapid wear of the chain and sprockets, it is customary to apply a greasy chain-lube via an aerosol. Many riders also fit aftermarket chain-oilers to feed a regular supply of oil to the chain at the rear sprocket. These chain oilers vary in sophistication, but all add significantly to the life of the chain. The custom of lubing by immersing the chain in a tin of hot grease ceased in the early 1970s, once most chains had rubber "O'-rings. The original Suzuki RE5 of 1975 came with a rear chain oiler, but the 1976 model had a sealed chain, and its oiler was deleted as "unnecessary".
A belt drive is still subject to stretch but operates very quietly, cleanly, and efficiently. A toothed belt is frequently used. However, they are not as durable when subjected to high horsepower as a chain. You can not alter the length and change final drive ratios as easily as chains. They also can not wrap as closely around as chains. And require larger pulleys compared to chain sprockets to get an effective final drive ratio. Replacing a drive belt typically requires removal of the swingarm, since belts cannot be split the way a chain with a master link can.
A shaft drive is usually completely enclosed; the visual cue is a tube extending from the rear of the transmission to a bell housing on the rear wheel. Inside the bell housing a bevel gear on the shaft mates with another on the wheel mount. This arrangement is superior in terms of noise and cleanliness and is virtually maintenance free, with the exception of occasional fluid changes. They are the most durable and usually last the life of the motorcycle. However, the additional gear sets are a source of power loss and added weight. A shaft-equipped motorcycle may also be susceptible to shaft effect.
Virtually all high-performance racing motorcycles use chain drive because they are the most mechanically efficient transmitting power to the rear wheel.
The wheel rims are usually steel or aluminium (generally with steel spokes and an aluminium hub) or mag-type cast or machined aluminium. Cast magnesium disks, produced by one-step hot forging from magnesium alloys ZK60 and MA-14, are also used for many motorcycle wheels.
At one time, motorcycles used wire wheels built up from separate components, but, except for dirtbikes, one-piece wheels are more common now. Performance racing motorcycles often use carbon-fibre wheels, but the expense of these wheels is prohibitively high for general usage.
Motorcycles mainly use pneumatic tires. However, in some cases where punctures are common (some enduros), the tires are filled with a tire mousse which is unpunctureable. Both types of tire come in many configurations. The most important characteristic of any tire is the contact patch, the small area that is in contact with the road surface while riding. There are tires designed for dirtbikes, touring, sport and cruiser bikes.
Dirtbike tires have knobbly, deep treads for maximum grip on loose dirt, mud, or gravel; such tires tend to be less stable and noisier on paved surfaces.
Sport or performance tires are designed to provide maximum grip for street use on paved surfaces but tend to wear faster.
Touring tires are usually made of a harder rubber compound for greater durability, these may last longer but tend to provide less outright grip compared to sports tires at optimal operating temperatures. Touring tires typically offer more grip at lower temperatures and can be more suited to riding in cold or winter conditions where a sport tire may never reach its optimal operating temperature.
Cruiser and "sport touring" tires try to find the best compromise between grip and durability. These tend to have stronger sidewalls as they are typically fitted to heavier machines.
Motorsport or racing tires offer the highest of levels of grip. Due of the high temperatures at which these tires typically operate, use outside a racing environment is unsafe, typically these tires do not reach their reach optimum temperature which provides less than optimal grip. In racing situations, tires are normally brought up to temperature in advance based on application and conditions through the use of tire warmers.
There are generally two independent brakes on a motorcycle, one set on the front wheel and one on the rear. However, some models have "linked brakes" whereby both can be applied at the same time using only one control.
Front brakes are generally much more effective than rear brakes: roughly two thirds of stopping power comes from the front brake—mainly as a result of weight transfer being much more pronounced compared to longer or lower vehicles, because of the motorcycle's short wheelbase relative to its center of mass height. This can result in brake dive.
Brakes can either be drum or disc based, with disc brakes being more common on large, modern or more expensive motorcycles for their far superior stopping power, particularly in wet conditions. There are many brake-performance-enhancing aftermarket parts available for most motorcycles, including brake pads of varying compounds and steel-braided brake lines.
In 1981, BMW introduced an antilock braking system (ABS) on a motorcycle. Other manufacturers have since also adopted this technology. ABS is normally found on motorcycles of 500 cc or greater engine capacity, although it is available on motor scooters down to 49 cc.
Fuel gauges are becoming more common, but traditionally a reserve tank arrangement is used with a petcock (petrol tap) on the side of the motorcycle allowing the rider to switch to a reserve fuel supply when the main fuel supply is exhausted. There is not actually a separate reserve tank: The intake for the petcock has two pipes, one extending higher into the fuel tank than the other. When fuel no longer covers the longer pipe the engine will lose power/splutter and the rider switches the petcock to the "reserve" setting, which accesses the shorter pipe. Riders whose bikes lack a fuel gauge (most machines prior to the past few years) usually learn how far they can go with a full tank of fuel, and then use a trip meter if available to judge when they must refill the tank.
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