dirt bikes

A motorcycle is a two-wheeled vehicle powered by an engine. Motorcycles are one of the cheapest and most widespread forms of motorised transport in many parts of the world.

On a typical motorcycle, the operator sits astride the vehicle on a seat, with the hands on a set of handlebars and the feet supported by footpegs. When the bike is at rest, the rider puts one or both feet on the ground. Engine speed is controlled by twisting the throttle on the right handlebar grip with braking being controlled with a hand lever and foot pedal. Shifting of gear ratios is controlled by operating a foot lever with the clutch being operated by a hand lever. Steering is accomplished by moving the handlebars.

History

The inspiration for the earliest dirtbike, and arguably the first motorcycle, was designed and built by the German inventors Gottlieb Daimler and Wilhelm Maybach in Cannstatt (since 1905 a city district of Stuttgart) in 1885. The first petroleum-powered vehicle, it was essentially a motorized bicycle, although the inventors called their invention the Reitwagen ("riding car"). They had not set out to create a vehicle form but to build a simple carriage for the engine, which was the focus of their endeavours.

However, if one counts two wheels with steam propulsion as being a motorcycle, then the first one may have been American. One such machine was demonstrated at fairs and circuses in the eastern US in 1867, built by Sylvester Howard Roper of Roxbury, Massachusetts. There is an existing example of a Roper machine dated 1869. It's powered by a charcoal-fired two-cylinder engine, whose connecting rods directly drive a crank on the rear wheel. This machine predates the invention of the safety bicycle by many years, so its chassis is also based on the "boneshaker" bike. In 1868, the Frenchman Louis-Guillaume Perreaux patented a similar steam-powered motorcycle, probably invented independent of Roper.

In 1894, the Hildebrand & Wolfmüller became the first motorcycle available for purchase.

In the early period of motorcycle history there were many manufacturers as producers of bicycles adapted their designs for the new internal combustion engine. As the engines became more powerful and designs outgrew the bicycle origins, the number of motorcycle producers decreased.

Until the First World War, the largest motorcycle manufacturer was the Indian. After that, this honour went to Harley-Davidson, until 1928 when DKW took over as the largest manufacturer. BMW motorcycles came on the scene in 1923 with shaft drive and an opposed-twin or "boxer" engine enclosed with the transmission in a single aluminum housing (photo left). In 1951, after the Second World War, the BSA Group became the largest producer of motorcycles in the world. The German NSU was the largest manufacturer from 1955 until the 1970s when Honda became the largest manufacturer, a title it retains to this day. British manufacturers (Triumph, BSA, Norton) held a dominant position in some markets until the rise of the Japanese manufacturers (led by Honda) in the late 1960s and early 1970s) who were able to produce designs more quickly, more cheaply, and of better quality.

Today the Japanese manufacturers, Honda, Kawasaki, Suzuki, and Yamaha dominate the motorcycle industry, although Harley-Davidson still maintains a high degree of popularity in America.

Recent years have also seen a resurgence in the popularity of many other brands including BMW, Triumph and Ducati, and the emergence of Victory as a second successful mass-builder of big-twin American cruisers.

Technical Aspects

Construction

The construction of modern motorcycles has mostly standardized on the following key components.

Chassis

The chassis (or frame) of a motorcycle is typically made from welded aluminium or steel (or an alloy) struts, with the rear suspension being an integral component in the design. Carbon-fiber and titanium are used in a few very expensive custom frames.

Some motorcycles include the engine as a load-bearing (or stressed) member; this has been used all through bike history but is now becoming more common.

Oil-in-Frame (OIF) chassis, where the lubricating oil is stored in the frame of the motorcycle, appeared for a while during the 1970s on some British motorcycles. It was widely unpopular and generally regarded as a bad idea at the time but has since gained some cache in modern (2006) custom bike world because of the space saving it can afford and the reference to an earlier era. [1]

Engine

Main article: motorcycle engine

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).

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 center to bottom dead center. To the layperson this is the "size" of the engine. Motorcycle engines range from 50 cc (cubic centimetres), commonly found in many small scooters, to 2294 cc, the largest production engine, currently made by Triumph for its Rocket III 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 today are the vertical single and twin, the V-twin, the opposed twin (or boxer), and the in-line triple and four.

Engines with more cylinders provide more power for the same displacement, and feel smoother to ride. Engines with fewer cylinders are cheaper, lighter, and easier to maintain. Liquid-cooled motorcycles have a radiator (exactly like the radiator on a car) which is the primary way their heat is dispersed. Water 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, whereas air cooled motorcycles are potentially cheaper, less mechanically complex and lighter weight.

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-strokes 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, air-cooled, and under 600 cc.

Transmission

Modern motorcycles normally have five or six forward gears. Only the largest touring motorcycles (most prominently, the Honda Goldwing) and a few models that are routinely used with a sidecar are fitted with a reverse gear. These motorcycles' weight (in the region of 300 kg) means they cannot effectively be pushed without the motor engaged.

The clutch is 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. 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 exploits mechanical advantage through a cable or hydraulic arrangement 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, either first or second gear can be selected, but higher gears may only be accessed in order - it is not possible to shift from second gear to fourth gear without shifting through third gear.

Final drive from the gearbox to the rear wheel is typically accomplished with a 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 buildup. Chains do deteriorate, and excessive wear on the front and rear sprockets can be dangerous. 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 is a tube extending from the rear of the transmission to a bell housing on the rear wheel. Inside the bell housing a bevelled 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. However, the additional gearsets are a source of power loss and add weight.

Scooters normally have a continuously variable transmission (CVT). CVT is a type of automatic transmission (also occasionally used in cars) that can change the "gear ratio" (gears are not generally involved) to any arbitrary setting within the limits. The CVT is not constrained to a small number of gear ratios, such as the 4 to 6 forward ratios in typical automotive transmissions.

Wheels

The wheel rims are usually steel or aluminum (generally with steel spokes and an aluminium hub) or 'mag' type cast or machined aluminum. At one time, motorcycles all used spoke wheels built up from separate components (see wheelbuilding), but, except for dirtbikes, one-piece wheels are more common now. Performance racing motorcycles often use carbon-fiber wheels, but the expense of these wheels is prohibitively high for general usage.

Tires

Motorcycles mainly use pneumatic tires. However, in some cases such as off-road motorcycles, the tires are filled with a type of mousse which helps prevent punctures. Both types of tires come in many configurations. The most important characteristic of any tire is the contact patch. That is 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 knobby, deep treads for maximum grip on loose dirt, mud, or gravel; such tires tend to be less stable on paved surfaces. Touring tires are usually made of harder rubber for greater durability. They may last longer, but they provide less grip (significantly less when cold, and the heavier rubber takes longer to warm up). Sport/performance tires provide amazing grip but may last 1,000 miles (1,600 km) or less. Cruiser and "sport touring" tires try to find the best compromise between grip and durability. There is also a type of tire developed specifically for racing. These tires offer unheard of levels of grip for cornering. Due to the high temperatures these tires typically operate at, use on the street is unsafe because the tires will not warm up (typically) by the time you arrive at your destination.

Brakes

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 powerful than rear brakes: roughly two thirds of stopping power comes from the front brake - mainly a result of weight transfer being much more pronounced compared to larger vehicles, due to the very short wheelbase . 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. There are many brake-performance-enhancing aftermarket parts available for most motorcycles including brake pads of varying compounds and steel braided brake lines.

In the 1980s, BMW introduced the antilock braking system (ABS) to the world of motorcycling. This life-saving advance has since been adopted for civilian motorcycles by some other manufacturers, including Honda, Suzuki, Yamaha, Kawasaki and Ducati. Some larger scooters also offer ABS brakes.

Suspension

Main article: Suspension (motorcycle)

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 generally consists of sliding aluminum tubes with long springs inside called forks which use hydraulic fluid for damping shock absorbers. For handling, the front fork is the most critical part of a motorcycle. The angle of rake determines how stable the motorcycle feels. 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 monoshock, which is mounted horizontally in front of the swingarm, below the swingarm pivot bolt

Instruments

With dirtbikes excluded, almost all motorcycles have a speedometer, an odometer and a tachometer. 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 long pipe, 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 many miles/km 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.

Fairing

A plastic or fiberglass shell, known as a fairing, is placed over the frame on some models to shield the rider from the wind. Drag is the major factor that limits motorcycle speed, as it increases at the square of the velocity, with the resultant required power increasing with the cube of velocity. As can be seen from the streamlined appearance of new performance motorcycles, there is much aerodynamic technology included in the design. Unfortunately, no one has been able to overcome the effect of the turbulence caused by the spinning front wheel, which prevents the motorcycle from cutting a clean path through the air. Another problem is that no designs have been discovered that can improve aerodynamic performance without unacceptably compromising the rider's ability to control the machine. 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. However, these motorcycles still effectively push their way through the atmosphere with brute force.

Cabin cycle solved the problem of aerodynamics by isolating driver from outside air.

Fuel efficiency

Motorcycle fuel efficiency benefits from the relatively small mass of the vehicle, compared to its passengers and to other motor vehicles, and subsequent small engine displacement. However, poor aerodynamics of exposed passengers and engines designed for goals other than fuel economy can work to reduce these benefits.

Fuel effiency varies greatly with engine displacement from a low of 29 mpg U.S. (8.1 L/100km) reported by a Honda VTR1000F rider^[1] to 107 mpg U.S. (2.2 L/100km) reported for the Verucci Nitro 50cc Scooter^[2]. A specially designed Matzu Matsuzawa Honda XL125 achieved 470 mpg U.S. (0.5 L/100km) "on real highways - in real conditions."^[3]

Dynamics

Main article: Bicycle and motorcycle dynamics

A motorcycle stays upright when it is steered to keep its center of gravity over its wheels. Lock the steering of a motorcycle and it is virtually impossible to ride. Cancel the gyroscopic effect of its rotating wheels by adding counter-rotating wheels, and it can still be easily ridden.

A motorcycle must lean in order to turn. This lean is induced by a method known as countersteering. This however is a separate action to the rider leaning their body, as it is virtually impossible to steer a motorcycle through body leaning alone.

Short wheelbase motorcycles, such as sport bikes, can generate enough torque at the rear wheel and enough stopping force at the front wheel in order to flip longitudinally. These actions, especially if performed on purpose are known as wheelies and stoppies respectively.

Social aspects

Subcultures

Around the world, motorcycles have historically been associated with subcultures. Some of these subcultures have been loose-knit social groups such as the cafe racers of 1950s Britain, and the Mods and Rockers of the 1960s. A few are believed to be criminal gangs.

Social motorcyclist organizations are popular, the most well known of these being the American Motorcyclist Association, Harley Owners Group, Gold Wing Road Riders (GWRRA), and BMW MOA. These motorcycle organizations have enthusiastic members, and many raise money for charities through organized events and rides. GWRRA and BMW MOA hold large international rallies in different parts of the United States or Canada every year that are attended by many thousands of riders.

Mobility

In many cultures, motorcycles are the primary means of motorized transport, not automobiles. According to the Taiwanese government "the number of automobiles per ten thousands population is around 2,500, and the number of motorcycles is about 5,000."^[4]

Safety

Main article: Motorcycle Safety

Motorcycles have a far higher rate of crippling and fatal accidents per unit distance than automobiles. According to the US Highway Safety Authority, in 2002 20.9 cars out of 100,000 ended up in fatal crashes. The rate for motorcycles is 66.7 per 100,000. The most common type of motorcycle accident is caused by inattentive drivers making a turn directly in front of a motorcycle. Other leading causes of motorcycle accidents involve unlicensed and untrained riders and drunk or drugged riding.

Why do people ride motorcycles when faced with these facts? The most common answer offered by students in courses designed by the Motorcycle Safety Foundation throughout the United States is "the feeling of freedom." They like the openness of motorcycling, compared to the enclosure of an automobile. They like feeling the wind and smelling the environment through which they ride. Riding a motorcycle, they say, "is like flying an airplane on the ground," and leaning into turns becomes the essence of motorcycling.

Motorcycles are also a very economical mode of transport, with advantages in ease of parking and ability to avoid heavy traffic.

But there is more. The visual appeal of a motorcycle, with its engine and elements visible, appeals strongly to motorcyclists. The design of motorcycles is a powerful attractant, witness the famous Art of the Motorcycle [2] exhibit at the Guggenheim Museum in New York City, which has traveled internationally.

The two major causes of motorcycle accidents in the United States are (1) motorists pulling out or turning in front of motorcyclists and violating their rights-of-way, and (2) motorcyclists running wide in turns and crashing. Both of these crashes are made more likely when motorcyclists mix any amount of alcohol with riding. Motorcyclists can do much to anticipate and avoid these crashes by getting proper training, by increasing their conspicuity to other traffic, and by separating alcohol and riding.

Types of motorcycles

Main article: types of motorcycle

There are many different types of motorcycles for many different purposes.

• Mopeds: small, light, inexpensive, efficient rides for getting around town. usually started by pedaling (motorcycle + pedals = moped).
• Dual-sport : A road legal machine offering the bare minimum of off road appearance, with little real suitablility for any "real" off road activity/terrain .
• Enduro: A road legal version of a motocross machine, ie featuring high ground clearness and copious suspension with minimal creature comforts. Highly unsuitable for long distance road travel. The few features that are different form the motocross versions are the silencers, the flywheel weights and the presence of features necessary for highway use.
• Scooters: bike with a step-through frame and generally smaller wheels than those of traditional motorcycles. Can be riden without straddling any part of the bike. Available in sport, commuter, and touring models.
• Sport bikes: Fast, light, sleek motorcycles designed for maximum performance, for racing homologation or spirited road riding. They are distinguishable by their brightly colored plastic bodywork and the rider's tipped-forward seating position.
• Cruisers: A range of small to large motorcycles designed for comfort and looks with a relaxed upright seating position. They are notable for their heavy use of chrome and are often highly customized.
• Choppers: Usually custom motorcycles with long rake (longer front forks) and wild paint jobs. These are created more for show than dependability and ridability.
• Touring motorcycles: designed for comfort, luggage carrying and reliability. Both cruisers and sport bikes can be used as touring bikes.
• Sport Touring: sport touring is hybrid of the sport bike and the touring motorcyle for those who desire the best of both of these worlds.
• Dirt bikes/motocross bikes/off-road bikes: designed for racing, recreation, or sometimes long-distance touring in gravel/mud/sand conditions.
• Pocket bikes: Small imitations of sport bikes designed for recreation or racing by all age levels; see Pocketbike Racing
• Mini bikes: Very small bikes deisgned to be simple and fun for children. Generally they have no clutch or shifting to simplify operation.

See also

• Category:Motorcycling
• Category:Motorcycles
• Category:Motorcycle technology
• Category:Motorcycle clubs
• Category:Motorcyclists organizations
• Category:Motorcycling events
• Category:Motorcycle racing
• List of motorcycle manufacturers

References

External links

• Motorcycle Safety Foundation
• Motorcycle
• UK Motorcycle News Site
• UK Directory & Legal Forum
• Japanese Motorcycle Wiki
• Motorcycle Videos
• Motorcycle Manufacturers history
• The V-Twin Forum The International Portal for V-Twin Motorcycle Enthusiasts
• The V-Twin Gallery The V-Twin Motorcycle Gallery
• motorcycle articles Riders community page