Motorcycle
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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 (either a single bar or or "clip-on"s which are used to steer the motorcycle, in conjunction with the rider shifting their weight through their feet, which are supported on a set of "footpegs" or "pegs" which stick out from the frame.
Variations exist: some motorcycles are equipped with floorboards instead of footpegs, and sidecars and other three-wheeled variations, commonly referred to as a trike may also be found.
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History
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The world's first motorcycle, designed and built by German inventors Gottlieb Daimler and Wilhelm Maybach in Cannstatt (a city district of Stuttgart) in 1885 was the first petroleum-powered vehicle ever. They called their invention Reitwagen ("riding car").
British manufacturers held a dominant position in some markets until the rise of the Japanese manufacturers (led by Honda) in the late 60's and early 70's who were able to produce designs faster and cheaper.
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 (or stressed) member; this has been used all through bike history but is now becoming more common.
The fuel tank is usually mounted above the engine. This tank is generally made of stamped, brazed or welded sheet steel, or blow-molded high-density polyethylene. At least one motorcycle manufacturer (Buell) offer models that use a hollow frame as the fuel tank, some British motorcycles designs used part of the frame as an oil reservoir. The wheel rims are usually steel, either with steel spokes and an aluminium hub, or 'mag' type sandcast aluminium. Performance racing motorcycles often use carbon-fibre wheels, but the expense of these wheels is prohibitively high for general usage.
A plastic or fiberglass shell, known as a fairing, is often placed over the frame, to shield the rider from the wind. Drag is the major factor that limits motorcycle speed, as it increases at the cube of the velocity. Despite the streamlined appearance of new performance motorcycles, there is still virtually no aerodynamic technology included in the design, and motorcycles still effectively push their way through the atmosphere with brute force. This is generally due to the fact 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.
Chassis stability
A good motorcycle chassis has no stability problems.
There could be three kinds of stability problems with motorbikes:
- Capsizing is well known in low speeds, and easy to overcome by going a bit faster.
- Wobbling ( http://www2.ee.ic.ac.uk/cap/cappp/projects/2/files/wobble_0_65.avi )is a high frequency (7-9 Hz) oscillation of the front wheel. It is often relatively harmless but annoying. It can appear at moderate speeds.
- Weaving ( http://www2.ee.ic.ac.uk/cap/cappp/projects/2/files/weave_0_65.avi ) is a low frequency (2-3 Hz) oscillation of the whole vehicle. It can become unstable at higher speeds with fatal results.
Based on http://www2.ee.ic.ac.uk/cap/cappp/projects/2/files/simosthesis.pdf :
- The weave oscillations damp out once the rider reduced the roll angle.
- Tyre characteristics and inflation pressures are important variables in the behaviour of the motorcycle at high speeds.
- From a stability point of view it is desirable to make the lateral stiffness as large as possible, with the possibility of an optimum value for the torsional stiffness of the rear frame.
- Common levels of lateral stiffness at the wheel spindle deteriorates the wobble mode damping substantially with significant changes in the wobble frequency as well, and slight reduction in the weave mode damping at high speeds.
- Lateral distortion should be opposed as much as possible by locating the front fork torsional axis as low as possible.
- The largest contribution to the weave damping came from the cornering and camber stiffnesses and relaxation length of the rear tyre and not so much from the same parameters of the front tyre.
- Amongst others, stiff frames, a long wheelbase, a long trail and a flat steering head angle were found to increase weave mode damping.
- Degraded damping of the rear suspension, rear loading and increased speed amplifies cornering weave tendencies.
- Rear load assemblies with appropriate stiffness and damping were successful in damping out weave and wobble oscillations.
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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. Over the years a variety of arrangements have been used at the rear from no suspension through to the current swingarm style. The wheels use pneumatic tires, generally characterised by a round profile, 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. In older motorcycles the rear may be on the left 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 and in some cases 100% depending on the model of motorcycle and operator; rear wheels can generally lock and skid much more easily than the front due to weight distribution dynamics. 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. Some manufacturers have created Antilock braking systems (ABS).
In virtually all cases, 70% to 90% of total braking force should be applied by the front brake when operated on a hard surface such as tarmac, 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 (and generally illegal) maneuver which requires practice to perfect. Trailbraking is a term used to describe carrying the braking action of a vehicle past the turn entry, allowing the rider to adjust speed all the way through a turn to the apex. Another variation of brake use can be seen at top level motorcycle roadracing and motorcross events. The technique of steering the motorcycle in a high speed turn (or lower speeds on a dirt course) using the rear brake is called "backing it in" (or "turning" on dirt). Racers while hard on the front brake will feather the rear brake just enough to start a controlled rear slide, thus rendering a sharper turn angle. Note: This technique is not recommended for public road use.
Engine
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The motor of a motorcycle typically sits immediately under fuel tank, between the rider's legs. Almost all commercially available motorcycles are piston driven internal combustion engines, with typical sizes between 50 cubic centimetres (cc) and 2300 cc. Larger motorcycles (above 500 cc) 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 generate power every other stroke, or once per revolution. Four stroke engines generate power for one stroke out of the four in the cycle, or once per two revolutions. Typically, two stroke engines deliver more power per unit of engine volume compared to four-stroke engines. However the four-stroke engine creates much more torque, specifically at lower speeds, and the maximum power of a two-stroke is concentrated over a narrow speed range ("power banding"). Two strokes are lighter for the same power, because of the mechanical simplicity, there are no valves as such, intake and exhaust are is controlled by the piston relative to "ports" in the cylinder wall. Four stroke engines have between two and five mechanically-actuated valves per cylinder, and the associated operating mechanism adds extra weight. Fuel-injected two-strokes can deliver good fuel-economy and comparably low emissions. Most two strokes require the addiiton of a combustible oil to the fuel to lubricate the cylinders, there being no oil below the piston. In California with its tough environmental laws, two-strokes are generally illegal because of their emissions. Two strokes are also usually much more fragile, and require far more frequent engine rebuilds. By comparison four-strokes are far more reliable, and therefore much more suited to everyday use.
Fuel injection now is widely available on commercially available motorcycles, but carburetors are still common. Computer-controlled engines are becoming the standard on the more advanced and expensive motorcycles, and can now even be found in small capacity engines, where emissions laws have prompted a move to fuel injection across the board.
Two and four cylinder engines are the most common; single cylinder engines are common on off-road bikes and small bikes / scooters. There are some 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. Ducati use what is described as an L-twin (the cylinders are arranged at 90° with one horizontal in the chassis) but all angles between the cylinders have been tried at some time in bike history. Some engines, of which BMW are typical are flat-twin (or "opposite twin") configuration. The cylinders are directly opposed to each other which leads to significantly less vibrations through the cancelling out of forces. Most four-cylinder engines are in-line rather than V-shaped and arranged transversely; the crankshaft is at an angle of 90 degrees to the frame. Ariel produced a "square four", consisting of two transverse parallel twin engines mounted in a common crankcase. While water cooling was rare before the last third of the 20th century, now water-cooled engines are common.
Motorcycle engines once had simpler auxiliary devices than car engines. Even when car engines had moved to coil ignition motorcycles kept with a magneto which generates its own power for the spark rather than needed a battery. Secondary coils could be be incorporated to power the lighting and also charge a battery. Modern motorcycle engines use alternators and coil ignition. Many modern motorcycle engines use highly sophisticated 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 twistgrip throttle on the right handlebar (where rotating the grip towards the rider increases air and fuel flow to the engine and so causes the bike to accelerate) and a gear lever at the left foot.
The gear lever operates by shifting gears when it is pressed or lifted. A normal street motorcycle is put in first gear by pressing the gear lever, while second and all further gears are reached by lifting it. Downshifting is done by pressing the gear lever. 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. In contrast, racing motorcycles have all gears arranged "below" the first gear, thus pressing the gear lever always shifts up, while lifting it shifts down.
Because there is no way to reach neutral without shifting to second or first gear, it is impossible to double-clutch on a motorcycle. This also means the rider always has to match the transmission speed to the ground speed - shifting to a gear too low for the motorcycle speed accelerates the transmission to a very high speed in only the time the gear shift takes, and would put a great force on the 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.
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 cogs 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 elongation (stretch) 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 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 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, cleanliness, and is virtually maintenance free. However, the additional gearsets are a source of power loss and add to bike weight.
Tires
Tires ('tyre' in the UK) 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 bikes. 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 (1,600 km) 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.
Motorcycle 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 street 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 forceful (and very possibly a 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. The use of an approved helmet is required by law in most countries.
Performance
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 can yield appreciable performance improvements, but this is often costly and very time-consuming. Improper attempts at tuning can yield benefits in one particular part of an engine's power band, while impairing performance everywhere else. Blueprinting, or restoring an engine to factory tolerances, can help to improve an engine's efficiency, and restore power that would otherwise be lost. Enlarging cylinder head ports, while common practice amongst many tuners, is often unnecessary (unless a big-bore kit has been fitted), to the extent that many engines benefit from decreasing the volume in the cylinder head. Done correctly, this increases the velocity of the fuel / air mixture entering the cylinder, packing more mixture in per revolution.
More usable improvements 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 performance 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, and therefore more suited to more specialised applications, usually racing (road or drag). Also, aftermarket exhaust systems are usually louder, by varying degrees, than stock systems. Most countries have limits on how much noise can legally be produced by vehicles, however this usually does not deter motorcyclists from fitting louder exhaust systems. There is even a school of thought that louder systems are safer, as they attract the attention of (car) drivers, who might otherwise have failed to notice the motorcyclist.
The most effective way of increasing power is forced induction. Turbochargers are generally more effective than Superchargers because they spin using the exhaust gases while a supercharger uses engine power to spin it, robbing power. Since more air is being forced into the engine, the air/fuel ratio must be changed to prevent the engine from running lean and/or destroying itself. On low boost settings, the turbocharger can increase power and fuel range. Engine internals such as pistons and connecting rods must be replaced with stronger ones. In addition, compression ratio must be considered as an "overboosted" engine will destroy itself as well.
With great care, a racing engine can be helped to "sprint" by injecting small amounts of Nitrous oxide. The main benefits of nitrous are three-fold;
- More oxygen is introduced into an engine's combustion chamber
- As N2O is stored in liquid form, it is still very cold when it evaporates and is mixed with fuel. This chilling effect raises the density of the mixture, packing more fuel and oxygen into the combustion chamber.
- This colder mixture helps to keep the engine running cooler, which is very useful as nitrous oxide is almost exclusively used in stressful, high RPM situations, primarily drag racing.
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 nitrous oxide injection. Using methods like nitrous oxide are fine on dragstrips, but are illegal on the street. In any case, a canister of nitrous oxide is rapidly expended, and impractical for sustained use on a road-going bike by any sane rider.
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. 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. Riders without a fuel gauge usually learn how many miles / km they can do with a full tank of fuel, and then use a trip meter if available to judge when they must refill the tank.
Motorcycle types
Road motorcycle
Road motorcycles are motorcycles designed for being ridden on the road. They feature smooth tires with a light tread pattern, and engines generally in the 125 cc and over range. Most are capable of speeds up to 160 km/h (100 mph), and many of speeds in excess of 200 km/h (122 mph).
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, which many find to be more comfortable for long-distance riding.
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. A true 'Chopper' is actually a cruiser pieced together from parts of other bikes, hence the term 'chop.'
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 owner's ideals, and as such are a source of pride and accomplishment.
Sportbike
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Sportbikes, sometimes called performance bikes, are typically much smaller and lighter than cruisers, and are essentially consumer versions of the motorcycles used in motorcycle racing, which they are generally only a few years behind. The riding position places the feet towards the back, the hands low and the spine inclined forward.
Sportbikes 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 or who have requirements of a smaller, lighter vehicle, smaller-displacement, sub-75 horsepower (56 kW) motorcycles are also manufactured. The many engine-sizes available often reflect the difference professional and amateur racing classes which adhere to strict engine-size and weight rules. The late 1990s saw "power wars" between various motorcycle manufacturers that culminated in Suzuki's 1300 cc GSX-1300R Hayabusa, the first production motorcycle to exceed 300 km/h, and Kawasaki's ZX-12R, designed to exceed 200 mph. Eventually a "gentlemen's agreement" was promoted by various European governments to limit production motorcycles to a maximum speed of 300 km/h (186 mph) in an effort to promote safety.
Sportbikes are sometimes called "bullet bikes", due to their light weight and high speeds, but this is considered derogatory; other slightly derogatory terms include "crotch rocket" and "plastic bikes" (owing to the fairing usually sported by these bikes). Many who operate these bikes, who wear bright colored racing clothing, are called "Power Rangers" by their detractors, due to their resemblence to the characters of the children's series Mighty Morphin' Power Rangers.
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), and a comfortable riding position. 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, but other notable examples include the Honda ST1100, the Honda Interceptor and the Kawasaki Concours, as well as more sport oriented options from Ducati to Buell. 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
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Also known as the "naked" bike or "street" 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 saw a resurgence at the end of the 1990s, with many manufacturers releasing new models with minimal or no fairings. The Yamaha FZ1, Honda 919, Honda 599 and Suzuki SV650 are popular examples of this style of motorcycle.
Large cylinder capacity versions of the "naked" type of motorcycle, are often referred to as "Muscle" bikes. Their main characteristics are vast amounts of torque and power, plus lower gearing compared to a "Sports" bike and an upright seating position. Models such as the Kawasaki ZRX1200, Yamaha XJ1300 and Suzuki GSX1400 fit this category. Most "Muscle" bikes also forgo modern fuel injection, computer management and monoshock suspension seen on the latest sports models, settling for more traditional carburettors and twin rear shocks.
Scooter
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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 Mediterranean Europe, particularly Italy, scooters are very popular thanks in part to their ability to squeeze down the narrow centuries-old streets that dominate the landscape and the good weather undoubtably helps. 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.
Moped
The moped is a hybrid between the bicycle and the motorcycle, equipped with a small engine (usually a small two-stroke engine up to 50 cc, but occasionally an electric motor) and a bicycle drivetrain, and motive power can be supplied by the engine, the rider, or both. In the UK these were subject to less stringent licensing than motorbikes and popular as very cheap motorbikes - the pedals seeing next to no use.
Dirt bike/Trials bike
Off-road motorcycles are designed for being ridden on rough terrain. They are known as "dirt bikes" and "trials bikes". An off-road motorcycle will typically have suspension with much more travel than a road bike, higher ground clearance and, hence, a higher center of gravity, tyres that are clamped onto the rims, (in some kinds of sports) only rudimentary seats (or none) and they have small (usually less than 700 cc) single-cylinder motors compared to the multiple-cylinder engines of road bikes.
Competitive dirt bikes are optimized for speed trials, enduros (long distance racing), hill climbing or timed-trials. In some countries, the most popular is the Motocross where several riders compete on a sand, dirt or mud track with banked corners, chicanes and large jumps that can put riders more than thirty feet in the air. Motocross bikes vary in class by engine size and engine type (2-stroke or 4-stroke). Common sizes vary from 50cc to about 650cc. Up to 250cc they are 2 or 4-stroke and above that they are 4-stroke.
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.
Trials bikes are used to negotiate difficult off-road courses—usually at quite slow speeds—and the rider's skills are assessed by whether a foot has to be placed on the ground to maintain the rider upright. Each step counts as points against. Good riders can negotiate swamps, streams and vertical banks, or rocks, of more than 2 metres height. It is not unusual to see riders mount truck trays and the topside of 20-foot containers without much of a ramp and without going much more than a bike-length onto the container.
Related to dirt bikes are dual-sport or "On-Off road" bikes which are street legal variants of dirt bikes with more suspension travel than a standard bike but having all the other equipment usually found on one.
Farm bike
These adaptions of trail bikes were first used by dairy farmers in New Zealand from the early 1960s. They wanted a light, simple machine that could be started easily and that would negotiate particularly muddy paddocks and steep hillsides in all weathers. A range of bikes were tried by a number of farmers and they came to use a mild-off-road machine that could carry a good load (mainly a tray for their dogs, instead of a rear seat) that was easy to mount, start and ride with heavy rainwear. Large profile low-pressure tyres with knobbly tread were found best for grass, mud and rocky tracks. Ultimately Japanese manufacturers developed a range of specialised bikes—about the time that the farmers came to use ATVs instead.
Derny
A Derny is a specialized type of motorcycle that is 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.
Towing
Although there are aftermarket trailers that allow motorcycle to tow, factory-made motorcycles specialized for towing are rare. The only known vechicle for towing is Retriever by a Swedish company named Coming Through, which is a modified version of Honda GL 1800 GoldWing. With the use of a high torque engine, low centre of gravity design, and retractable trailer, towing motorcycles can reduce response time for retrieving cars and light trucks on congested roads.
Model naming schemes
Each manufacturer creates their own naming scheme with varying numbers, letters, and names.
Manufactures often release what is basically the same model of bike for multiple markets with differing names. For example, one model of Honda motorcycle is named the Fireblade[1] (http://www.honda.co.uk/motorcycles/DispatcherServlet?hidActionDetail=viewproductdetail&hidAction=Lookup&hidProductID=68&hidSelectedProductCode=CBR1000RR&hidProductName=CBR1000RR+FireBlade&hidMSGID=8&hidMSGCode=SUPERSPORTS&hidMSGName=Supersports&hidBannerPath=en%2Fpicture%2Fproduct%2FCBR1000RR%2FMain%2Fprd_main_Banner.jpg&hidHomePath=%2Fjsp%2FmsgSUPERSPORTSHome.jsp) in Europe, while in the U.S. it is named the 1000RR[2] (http://powersports.honda.com/motorcycles/sport/model.asp?ModelName=CBR1000RR&ModelYear=2005&ModelId=CBR10RR5).
![[1]](http://www.honda.co.uk/motorcycles/DispatcherServlet?hidActionDetail=viewproductdetail&hidAction=Lookup&hidProductID=68&hidSelectedProductCode=CBR1000RR&hidProductName=CBR1000RR+FireBlade&hidMSGID=8&hidMSGCode=SUPERSPORTS&hidMSGName=Supersports&hidBannerPath=en%2Fpicture%2Fproduct%2FCBR1000RR%2FMain%2Fprd_main_Banner.jpg&hidHomePath=%2Fjsp%2FmsgSUPERSPORTSHome.jsp){kind=link}
Some naming schemes are based on engine size. Most manufacturers follow this almost religiously except where it pertains to "cruiser" style models.
Harley Davidson has a unique naming scheme that has evolved over the company's existence. It's complex and confusing to anyone who isn't steeped in "Harley" lore. In their defense, Harley Davidson as a company has come quite a long way in simplifying this even while their motorcycles retain the same basic design they utilized in the 1950s.
Safety
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 clothing is also often mandated, especially a helmet. Other protective gear include jackets, gloves, boots, and pants. The jackets range from nylon to leather and, the more advanced, kevlar. Some jackets include heavy padding on elbows, spine and shoulder regions. Gloves are generally made of leather or kevlar and some include carbon fiber knuckle protection. Boots, especially those for sport riding, include reinforcement and plastic caps on the ankles, and toe area. Pants are usually leather, nylon or kevlar. One company even makes a pair of jeans with kevlar reinforcement. None of these items are required by law in any state (in the U.S.) but are recommended by many of those who ride. Trail-bike riders wear a range of plastic armour to protect against injury from falling off, hitting other riders and bikes and from running into track barriers protecting the public. The armour protects the extremities from breakage and disjointing and the back and chest from strain and broken bones. Although efficient it is not always effective.
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. Given that generally motorcycles cover less distance than cars per year the figure per unit distance is likely to be much worse.
Noise Pollution
Like any internal combustion engine powered vehicle, motorcycles have the potential to generate noise pollution. Both unmodified sports bikes and DIY modifications to the exhaust systems of the smallest motorbikes can contribute. In general legislation exists to limit noise in many countries but the higher pitch, due to the higher engine speeds, is perceived as more intrusive.
The a study by in 1979 by Bondello and Brattstrom found that motorcylce noise has caused the defeaness of desert iguanas and kangaroo rats, which are now endangered species. According to the publication,"Health Effects from Environmental Noise Exposure" by Evelyn Talbott and Shirley Jean Thompson, noise pollution from things like motorcycles causes increases in cardiovascular disease from elevated blood pressure, and physiological reactions involving the cardiovascular endocrine system. It causes sleep disturbances and destroys mental health. It disrupts the ability of communication, performance and behaviour, reading and memory acquisition.