Motorcycle

A motorcycle (or motorbike) is a two-wheeled vehicle powered by an engine. The wheels are in-line, and at higher speed the motorcyle 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.

Motorcycles have a far higher rate of crippling and fatal accidents than automobiles do per mile. This is due to the exposed rider, the lack of restraints, and also the fact that many automobile drivers are not accustomed to frequently sharing the road with motorcycles.

A gas-powered motorcycle was invented by the German inventor Gottlieb Daimler in 1885.


A 125 cc motorcycle, the Italian-manufactured Cagiva Planet.

Control

The motorcycle's steering is controlled by the handlebars and the rider's positioning. At speeds lower than 20-25 MPH, motorcycles will feel like they steer, but all turns on two wheeled vehicles are initated by a gentle press in the direction of the turn. At lower speeds, however, the handlebars will come around in the direction of the turn, creating the impression of steering. At higher speeds, the gyroscopic forces cause a phenomenon known as "counter-steer" to occur, where (for instance) pushing on the left handlebar and pulling on the right will cause the bike to lean to the left, and then execute a left hand turn. Turning cannot similarly be executed by changing body position, but can been used in conjunction with countersteering.

Gyroscopic precession of the front wheel causes 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.


Yamaha FJ1200 1200cc motor cycle,
registered 1992


Construction

Chassis

The chassis of a motorcycle is typically made from welded aluminium or steel struts, with the rear suspension being an integral component in the design.

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, their 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.


An English motorcycle from 1966, the 250cc Ariel Leader

Suspension

The two wheels of a motorcycle are connected to the chassis by a suspension arrangement. The front suspension generally consists of sliding steel tubes with long springs inside, using hydraulic fluid for damping shock absorbers, however a variety of arrangements are used on the rear. The wheels use pneumatic tires, generally characterised by a rounded surface, to ensure good traction while leaning as described above. Correct tire pressure and correct adjustment of suspension are essential to safe cornering, far more so than in a four wheeled vehicle, as any loss of grip can lead to loss of control of the motorcycle.

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.

Brakes

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. The front brake is generally much more powerful than the rear as between 70% to 90% of stopping power (depending on the design of the motorcycle) 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. Common misconceptions with motorcycle brakes include fear that aggressive use of the front brake will stop rotation of the tyre and cause loss of control, or a skid. There is a phenomenon known as a "stoppie" which can only be achieved if the front brake is used aggressively with no application of the rear brake, and the chassis is raised clear of the roadway while still travelling forward on the front wheel - this is a highly skilled manoever and needs painful practice to perfect so *do not attempt this on occupied roadways*. The more common, current misconception is that application of the rear brake will cause motorcycle instability. In virtually all cases, motorcycle brakes should be used similtaneously with 70% to 90% of brake pressure being used on the front brake and the remaining pressure being used on the rear brake.

Engine

The motor of a motorcycle typically sits immediately under the gas tank, between the rider's legs. Almost all commercially available motorcycles are piston driven internal combustion engines, with typical sizes between 50cc and 1800cc. Larger motorcycles (above 500cc) on the modern market are mostly four stroke engines, but there is a sizable minority of two stroke engines on smaller motorcycles.

Two stroke engines have almost twice as much power per CC of displacement as four-cycles, 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.

Transmission

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.

Tires

Tires come in many configurations, the most important part of any being the contact patch. That is the small area that is in contact with the road surface while riding.

There are tires designed for dirtbikes, sport, cruiser, and touring. Touring tires are usually harder rubber and last longer but provide less grip, cruiser tires occasionally have raised white lettering, while sport/performance tires provide amazing grip but may only last 1,000 miles or less. Sport Touring tires try to find the best compromise between grip and durability.

Tires should be maintained at the proper air pressure at all times, and usually have a life expectancy of four to five years. Small cracks on the sidewall are an indicator of replacement time, as well as bald spots. A 'sticky' tire, one close to roadracing compound, will wear faster but will give a much better grip on the road. A touring tire takes longer to warm up and can lose its grip on cold, damp roads.

Motorcylce tires can also be found in "Race" compounds. However, race compound tires should NOT be used in street applications. Race compounds are designed specifically for the short life and few heat cycles of a race environment where street "DOT" tires are designed for multiple heat cycles and use in a street environment. In most cases, riders will actually achieve higher levels of performance using DOT street tires than race compounds.

If a tire loses grip, the rider may crash and make contact, in a rather painful manner, with the road or other obstacles. The motorcyclist must, therefore, consider proper motorcycle attire, such as helmet, gloves, boots, armored jacket and pants. Wearing a t-shirt, shorts, and sandals on a motorcycle is not advised.

Tuning

There are several ways to increase speed.

The most efficient way to improve the handling and speed of a motorcycle is to properly maintain the performance of the most critical element of the motorcycle; the operator. By attending riding schools and increasing rider education levels, a motorcyclist will be able to ride safely.

The next-largest cause of loss of speed is rolling resistance. The right tires kept at the proper pressure will contribute to both speed and safety.

On the engine, keep the air filter and chain clean, use high-quality lubricants and fuel with precisely-tuned spark plugs, mixture and timing. This is obvious, but often neglected.

Engine modifications should be considered as a last resort to gain performance. In many cases the addition of high performance exhaust systems, porting and polishing of the heads and other methods will actually DECREASE engine performance.

More improvement can be had by improving and upgrading suspension components. Suspension is typically the one element of the motorcycle that will receive the least amount of attention from the factory. Replacing stock shocks, fork springs and changing damping and valving rates will result in dramatic improvements in motorcycle stability and increased speed and rider confidence as a result.

Another way to increase performace is to have a tuned exhaust system. This helps evacuate the engine rapidly, and permits a longer power-stroke. However many production bikes already have tuned exhausts. A "custom" tuned exhaust will often operate only at a narrower range of engine RPM-- exellent for racing. Also, exhaust systems that produce more that 80db of sound are illegal for street applications.

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.

Instruments

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.

Motorcycle Types

Road Motorcycle

Road motorcycles are motorcycles designed for being ridden on the road. They feature smooth tires, and engines generally in the 250cc and over range. Most are capable of speeds up to 160 km/h, and many of speeds in excess of 200km/h.

Road motorcycles are themselves broken down into several sub-categories.

Cruiser

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 Bike

These motorcycles are visually similar to machines used in motorcycle racing and are generally only a few years behind the real racing machines. The riding position places the feet towards the back, the hands low and the spine inclined forward.

Sports/Performance bikes are powerful machines capable of high speeds with great stability in corners. Large displacement sports bikes offer tremendous power to weight ratios and newer riders with less experience should never fool themselves into thinking these machines are rideable. Newer riders should always start with smaller displacement, sub-75 horsepower, motorcycles. In the late 1990's the horsepower wars between the different bike manufacturers heated up to a fever pitch. Eventually a "gentleman's agreement" was promoted by various European governments that would limit production motorcycles to a maximum of 186 horsepower in an effort to save the lives of those who end up buying more motorcycle than they should handle.

Sport Bikes are sometimes referred to as "bullit-bikes". The term Bullit-Bike is a very derogatory term and found to be very offensive to riders of sport/peformance motorcycles. In the U.S.A. sport bike are also often known, generally by non-riders, as "crotch rockets".

Touring and Sport Touring

Touring motorcycles are characterised by wind protection for the rider (in the form of a fairing or windscreen), high capacity fuel tanks (for extended riding distances), and the ability to carry some amount of luggage (usually in the form of panniers and/or a topbox mounted towards the rear of the motorcycle). Although any motorcycle can be so equipped and used to tour with, specialised touring motorcycles such as the Honda Goldwing have become increasingly popular. Sport tourers are a hybrid form between sporting bikes and tourers and allow long-distance riding at higher speeds - the first example of this type of motorcycle was the BMW R100RS. Another hybrid is the custom tourer, which combines cruiser and tourer characteristics - the original form of this type is the Harley-Davidson Electra-Glide.

Standard

Also known as the "naked" bike, this is the basic form of the motorcycle stripped down to its fundamental parts. The emphasis is on functionality, performance and ergonomics rather than flashy body panels and exaggerated riding positions that are most common on sport bikes. This style of motorcycle has seen a resurgence as at the end of 1990's, with many manufacurers releasing new models with minimal or no fairings. The Yamaha FZ1, Honda 919 and Suzuki SV650 are popular examples of this style of motorcycle.

Scooter

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" diameter), automatic transmissions, small (generally less than 125cc) 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 250cc 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.

Moped

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.

Dirt Bike

Off-road motorcycles are motorcycles designed for being ridden in rougher terrain. They are also known as "dirt bikes" and "trail bikes". An off-road motorcycle will typically have suspension with more travel than a road bike, higher ground clearance and hence a higher centre of gravity, and a small (less than 500cc) single cylinder motor.

Competitive dirt bikes are optimized for speed trials, enduro (long distance racing), hill climbing, or timed-trials. Some authorities think that the competition that best reflects real-life needs is the timed trials, because they require a balance of maneuverability, speed, light weight and reliability.

Derny

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.

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