A motorcycle (or motorbike) is a two-wheeled vehicle powered by an engine. The wheels are in-line, and at higher speed the motorcycle remains upright and stable by virtue of gyroscopic forces; at lower speeds continual readjustment of the steering by the rider gives stability. The rider sits astride the vehicle on a seat, with hands on a set of handlebars which are used to steer the motorcycle, in conjunction with the riders weight shift through their feet which are supported on a set of "footpegs" or "pegs" which stick out from the chassis.
Variations exist: some motorcycles are equipped with floorboards instead of footpegs, and sidecars and other three-wheeled variations may also be found.
Gyroscopic precession of the front wheel is one of the phenomena that cause both counter-steer, and steering by leaning. The turning wheel rotates the effect of a force applied to the wheel by ninety degrees. So, counter-steer happens because pressing on the left handlebar applies a rightward force on the front of the wheel, and a leftward force on the back of the wheel. The wheel's motion is rotated ninety degrees: the top of the wheel (ninety degrees from the back) moves left, leaning the bike. Leaning the bike left causes the front of the wheel (ninety degrees from the top) to steer to the left.
Other important factors are the inclination of the steering stem (Rake) which combined with the offset of the fork yokes means that the steering axis of the front wheel meets the ground at a point in front of the contact point of the tyre. In this respect the front wheel will act like a castor. The distance between the contact point of the tyre and the point at which the steering axis intersects the ground is called the Trail.
The fact that rider inputs have an enormous influence on the steering of two wheelers can be seen by anyone who has seen a delivery boy riding a bicycle "no hands". Here counter steering is clearly not a factor. Similarly stunt riders are able to ride long distances and negotiate corners, often at high speed, with the front wheel in the air.
Some motorcycles include the engine as a load bearing member; this is becoming more common.
The gas tank is usually mounted above the engine. The gas tank is made of either stamped, brazed sheet steel, or blow-molded high-density polyethylene. Newer models are using the frame itself as the gas tank. The wheel rims are usually steel, either with steel spokes and an aluminum hub, or 'mag' type sandcast aluminum. Racing applications occasionally use carbon fiber as wheel material.
A fairing is often placed over the frame, to shield the rider from the wind. Drag is the major factor limiting motorcycle speed as it increases at the cube of the velocity. Despite the streamlined appearance of new performance motorcycles, there is virtually no areodynamic technology included in the design. Motorcycles still have to push their way through the atmosphere with brute force. In the absence of a fairing or windshield, a phenomenon known as the windsock effect occurs at speeds above 100 km/h, where the rider becomes a major source of drag and is pushed back from the handlebars, tiring the rider.
The front fork is the most critical part of a motorcycle. The angle of rake determines how controllable the steering is. The rake should be chosen so that precessive force from countersteer and leaning-steering slightly overbalance the leaning forces from the weight of the bike, at a speed near the running speed of a person. This is the speed at which feet can no longer be safely used to balance a bike.
The rear shock absorber(s) control rebound and damping, and are attached from the frame to the swingarm. Dual shocks are placed at the far ends of the swingarm, and the monoshock is placed at the front of the swingarm.
There are generally two independent brakes on a motorcycle, one set on the front wheel, controlled by the right hand lever, and one on the rear controlled by the right foot. However, many models have "linked brakes" which apply both at the same time, although one more than the other. The front brake is generally much more powerful than the rear as roughly 2/3rds of stopping power can come from the front brake when properly applied; rear wheels can generally lock and skid much more easily than the front. Brakes can either be drum or disc based, with disc brakes being more common on large, modern or expensive motorcycles for their far superior stopping power, particularly in wet conditions. Some manufacturers are creating motorcycles with ABS; others are creating linked brakes which actuate both rear and front brakes (although perhaps with different strengths) when either lever is depressed.
In virtually all cases, 70% to 90% of total braking force should be applied by the front brake, with the remainder being simultaneously applied to the rear brake. Riders fear that aggressive use of the front brake will stop rotation of the tire and cause loss of control, or a skid, and therefore often fail to use the front brake to its full potential. Another common misconception is that application of the rear brake will cause motorcycle instability. The phenomenon known as a "stoppie" may only be achieved if the front brake is used aggressively with no application of the rear brake; if sufficient force is applied to the front brake, the rear of the motorcycle chassis will lift off the roadway, while the bike continues to move forward on the still-rotating front wheel. This is a highly skilled maneuver which requires practice to perfect.
Two stroke engines have almost twice as much power per cc of displacement as four stroke engines, because they generate power on each stroke. Two strokes are also lighter, for the same power, because the valves that control intake and exhaust are not mechanical, being on the sides of the piston. Four stroke engines have between two and five valves per cylinder, and must have mechanically-actuated valves, springs, cam-shafts, chains, and gearing to operate them properly, with the attendant extra weight of that equipment. Fuel-injected two-strokes even get good fuel-economy and comparably low emissions. Most two strokes inject special combustible oil into the gasoline to keep the cylinders lubricated. In California, two-strokes are generally illegal because of their poorer emissions.
Fuel injection is widely available on commercially available motorcycles, but carburators are still common. Computer-controlled engines are becoming the standard on the more advanced and expensive motorcycles.
Two and four cylinder engines are the most common available; single cylinder engines are common on off-road bikes and small scooters. There are commercially available three cylinder designs, and even a few five and six cylinder and V8 models. Two cylinder engines are most commonly found in either a "V-twin" configuration or a "parallel-twin" configuration. Most four-cylinder engines are in-line rather than v-shaped and arranged transversely, that is, the crankshaft is at a 90 degree angle to the frame. Both water-cooled and air-cooled engines are common.
Motorcycle engines once had simpler auxiliary devices than car engines.
Most notably, in the early years, the ignition system and battery charging were often provided by a magneto, rather than a coil and points system. A magneto has a special generator with a large number of turns on its coil. The generator directly produces the spark. Usually a secondary coil produces electricity to charge a battery. The battery charging coil's current was not as steady as a car's generator. Modern motorcycle technology is as used with automobiles - alternators generate AC volts and this is rectified into 12 volts DC. Many modern motorcycle engines use highly sophistocated electronics, notably in engine management and fuel injection systems.
The transmission is controlled by a clutch lever under the left hand in standard configurations, a throttle on the right handlebar (where pushing the wrist down increases fuel to the engine and so causes the bike to accelerate) and a gear lever at the left foot. The gear lever typically operates by downshifting when the lever is depressed, and upshifting when the lever is lifted; neutral sits between first gear and second, so a small lift out of first causes the gearbox to change into neutral, but a large movement causes the gearbox to change into second gear. Modern motorcycles normally have five or six forward gears. Only the largest touring motorcycles and a few models that are routinely used with a sidecar are fitted with a reverse gear.
The clutch is typically an arrangement of plates stacked in alternating fashion, one geared on the inside to the engine, and next geared on the outside to the transmission input shaft. Whether wet (rotating in engine oil) or dry, the plates are squeezed together by a spring, causing friction buildup between the plates until they rotate as a single unit, driving the transmission directly. A lever on the handlebar, through a cable or hydraulic arrangement, uses mechanical advantage to release the clutch spring, allowing the engine to freewheel with respect to the transmission.
The most commonly used transmission is a sequential gearbox. From neutral, you may select either first or second gear, but higher gears may only be accessed in order - you may not shift from second gear to fourth gear, without shifting through third gear. Internally, a rotating cam on the shift lever operates dogs on two counter-rotating shafts carrying a variety of gears. One shaft is geared to the final drive mechanism, and the other to the clutch. Operating the shift lever slides individual gears on one shaft, to intersect with a matching gear on the other. The small mass of the whole arrangement allows for extremely quick gear changes. Also, gear synchronizers typically found in passenger cars with manual transmissions are not necessary. The two shafts are always geared together (except in neutral), always spinning at a speed nearly approximating the next higher or lower gear ratio. Aided by beveled edges on the gears, shifting gears is simple for novices - no double clutching or grinding of gears. Advanced drivers can perform "full-throttle upshifts" on racing mounts, but this risks both the warranty and mechanical integrity.
Final drive from the gearbox to the rear wheel is typically accomplished with a chain, which requires both lubrication and adjustment for stretch. The lubricant is subject to being thrown off the fast-moving chain and results in grime and dirt buildup. Chains do deteriorate, and excessive wear on the front and rear sprockets can be dangerous. Many motorcyclists replace the chain and both sprockets as a set to maintain efficiency and safety. Many manufacturers offer cruiser models with final drive options of a belt, or a shaft. A belt drive is still subject to stretch, but operates very quietly, cleanly, and efficiently. However, belt drives are limited in the amount of power they can transmit. The belt is frequently toothed. A shaft drive is completely enclosed, the visual cue a tube extending from the rear of the transmission to a bell-housing on the rear wheel. Inside the bell housing a beveled gear on the shaft mates with another on the wheel mount, typically packed in a high-quality grease or floating in oil, in a sealed compartment. This arrangement is superior in terms of noise, cleanliness, and is virtually maintenance free. However, the additional gearsets can rob the system of power, and do weigh a bit more.
With great care, a racing engine can be helped to "sprint" by injecting small amounts of nitromethane. Nitromethane adds power because it doesn't need air to burn. Engines using large amounts need precise mixtures, or configurable timing and carburation. It's very easy to blow the gaskets or burn the valves of your expensive, custom-tuned engine with careless nitromethane injection. Using methods like nitromethane are fine on dragstrips, but are illegal in many areas.
Almost all motorcycles have a speedometer and odometer and many have a tachometer. Fuel gauges are becoming more common, however traditionally a reserve tank arrangement has been used with a tap on the side of the motorcycle allowing the rider to switch to a reserve fuel supply when the main fuel supply is exhausted; this is typically done while the vehicle is in motion. There is not actually a separate reserve tank, the intake for the tap has two pipes, one longer than the other, when fuel no longer covers the long pipe the rider switches to the shorter pipe.
These motorcycles mimic the style of American machines from the 1930s to the early 1960s, such as those made by Harley-Davidson, Indian, Excelsior and Henderson, even though they have benefited from advances in metallurgy and design. The riding position places the feet forward and the hands up, with the spine erect or leaning back slightly. Cruisers are often used to signal adherence to a lifestyle committed to freedom, the most extreme form of which is found in motorcycle gangs such as the Hell's Angels.
Choppers are extreme cruiser configurations where the handlebars rise to a level above the riders shoulders with very long forks. They are notable for their extreme looks and equally extreme handling characteristics.
Some cruisers may have limited performance and turning ability because of a low slung design. Riders who enjoy cornering at higher speeds may need to customize to enhance lean angle, or start with a performance cruiser. Cruisers are often custom projects that result in a bike that suits the owners ideals, and as such are a source of pride and accomplishment.
Sports bikes are almost invariably capable of very high speeds, with great stability in corners. Large-displacement sports bikes offer large Power-to-weight ratio and are difficult to manage by those not experienced in their operation; for the less-experienced, smaller-displacement, sub-75 horsepower (56 kW) motorcycles are also manufactured. The late 1990s saw "power wars" between various motorcycle manufacturers that culminated in Suzuki's 1300 cc Hayabusa, the first production motorcycle to exceed 300 km/h, and Kawasaki's ZX12R, designed to exceed 200 mph. Eventually a "gentleman's agreement" was promoted by various European governments to limit production motorcycles to a maximum speed of 186 mph (300 km/h) in an effort to promote safety.
Sports bikes are sometimes called "bullet bikes", due to their light weight and high speeds, but this is considered derogatory; in the USA the derogatory term "crotch rocket" is also sometimes used.
Scooters are similar to motorcycles and are also designed for being ridden on the road. They are characterized by smaller wheels (generally less than 14 in (357 mm) diameter), automatic transmissions, small (generally less than 125 cc) engines, and a step-through configuration allowing the rider to ride with both feet on a running-board and knees together. In Europe, scooters are very popular thanks in part to their ability to squeeze down the narrow centuries old streets that dominate the landscape. In the United States scooters have long been a fixture on college campuses and strapped to the back of Recreational Vehicles due to their portability and exceptional fuel economy. However much larger scooters with engine displacements greater than 250 cc are becoming more popular. The Honda Silver Wing, Honda Reflex, and Suzuki Burgman are the most popular "maxi-scooter" models available in the United States.
The moped is a hybrid between the bicycle and the motorcycle, being equipped with an engine (usually a small two-stroke engine, but occasionally an electric motor) and a bicycle drivetrain, and motive power can be supplied by the engine, the rider, or both.
A Derny is a specialized type of motorcycle designed and built for use in track cycling events where a derny driver blocks the air-resistance for a racing bicycle riding close behind the derny.
Motorcycles have a far higher rate of crippling and fatal accidents per unit distance than automobiles. This is due to the exposed rider and the fact that many automobile drivers fail to see these smaller vehicles in the traffic stream. In many developed countries riders are now either required or encouraged to attend safety classes in order to obtain a separate motorcycle driving license. The wearing of protective gear is also often mandated, especially Source | Copyright
