Frames

Motorcycle frames are usually made from welded aluminium, steel or alloy, carbon-fibre is used in some expensive or custom frames. The purpose of a motorcycles frame is to act as a base onto which all the various components can be bolted to. The engine generally sits inside the frame, the rear swingarm is attached by a pivot bolt (allowing the suspension to move) and the front forks are attached to the front of the frame. The frame can also help to protect the more sensitive parts of a motorcycle in a crash.Buell, one of the motorcycling world's greatest innovators, uses the frame as a fuel tank on many of it's models like the XB12S Lightning.The various types of frame commonly used include.

Single cradle frame. The single cradle is the simplest type of motorcycle frame, and looks similar to the first ever motorcycle frames. It is made from steel tubes that surround the engine with a main tube above and other, smaller diameter tubes beneath. If a single cradle becomes double at the exhaust, as frequently occurs, it is referred to as a split single cradle frame. Single cradle frames are usually found in off-road motorcycles.

Double cradle frame. Double cradle frames are descended from single cradle frames. They consist of two cradles that support the engine one either side. Double cradle frames are commonly used in custom motorcycles and simpler road bikes. They offer a good compromise between rigidity, strength and lightness, though they have now been technically surpassed by perimeter frames.

Backbone frame. Far from the most desirable frame around, the backbone frame comprises a single, wide main beam from which the engine is suspended. The backbone frame allows for great flexibility in design, since it is concealed inside the finished motorcycle. The engine just seems to hang in mid air. It is simple and cheap to make, and is used mainly on naked and off-road motorcycles. 

Perimeter frame. Motorcycle racing research has shown that major advantages are to be gained in terms of rigidity by joining the steering head to the swingarm in as short a distance as possible. Flexure and torsion are dramatically reduced. This is the concept behind the perimeter frame. Two robust beams descend in the most direct way possible from the steering head to the swingarm, passing around the engine. The earliest perimeter frames were made from steel, but the need to improve rigidity to weight ratios led most manufacturers to adopt aluminium instead. Aluminium is now by far the most common road bike frame material and the aluminium perimeter frame is the most popular frame for modern supersports motorcycles. 

monocoque frame. The monocoque frame is used nearly exclusively on competition bikes and is very rarely found on road-going bikes. Monocoque frames act as a single piece unit that functions as seat mounting, tank and tail section. Though they offer certain advantages in terms of rigidity, monocoque frames are heavy and generally not worth the effort.

Trellis frame. The trellis frame rivals the aluminium perimeter frame for rigidity and weight. A favorite of Italian and European manufacturers it has proved a great success in racing and competition. The Trellis frame uses the same principles as the perimeter frame, and connects the steering head and swingarm as directly as possible. The frame is made up of a large number of short steel (or aluminium) tubes welded together to form a trellis. The trellis frame is not only easy to manufacture but extremely strong as well. The frame pictures is from the Suzuki SV650S.

Engines

Two-stroke engines

The two-stroke engine cycle differs from the more common four-stroke cycle by having only two strokes (linear movements of the piston), although the same four operations (intake, compression, power, exhaust) still occur. Thus, there is a power stroke per piston for every engine revolution, instead of every second revolution.Two-stroke engines are light, mechanically simple and produce more power than a similar size four stroke when running well. The down sides of a two-stroke are: They are oily and dirty, require regular maintenance, and power is only available in a narrow rpm band, often referred to as the power band. Two stroke sportbikes like the Aprilia RS250 are well known for their acute handling, lightweight, and narrow powerband, unfortunately they are no longer produced.

Four-stroke engines

Four-stroke engines are by far the most common type of engines found in modern motorcycles. The four-stroke engine operates on the exact same principle as regular car engines except on a smaller scale. Four-strokes are cleaner, more reliable and power comes across a much wider range of rpm than two-strokes.

The two strokes first, intakeand compression, second, combustion and exhaust.

Engine Configuration

Engines come in a variety of cylinder configurations and numbers. Some general rules which most engines live by are: More cylinders usually allows for a higher maximum rpm. Less cylinders provide more torque at low rpm. And vibrations tend to decrease with more cylinders.

One cylinder, or single cylinder engines as they are commonly known, are just that. One cylinder, usually positioned vertically with a single spark plug attached to the top.

Two cylinder engines, or twins, are one of the most popular types of motorcycle engine. V-twins are the most common 2 cylinder engines, the cylinders are positioned in a 'V' configuration with both cylinders pointing upwards, V-twin engines power all Harley-Davidson bikes and many sportbikes with 'character'.L-twin engines power some Ducati motorcycles, this is essentially a V-twin with one cylinder pointing horizontally forward.Parallel twins exist where the cylinders are positioned parallel to one another.BMW produces boxer twin (otherwise known as flat twin) engines. In a boxer twin engine the cylinders are opposed to one another and move in a manner similar to a boxers fists.

Three cylinder engines, or triples are less common. However, companys such as Triumph and Benelli have produced several triple engines. Triumph has cornered the market in triples and their newest sportsbike the Daytona 675 Triple is one of the most desirable bikes on

V-twin engine                      BMW Boxer twin

the market today.

Four cylinder engines are similar to small car engines, the cylinders are normally positioned in an in-line configuration, where the cylinders are lined up one after another in a line. V and square twin designs have also been produced.

A less conventional motorcycle engine, comes in the MTT Y2K Turbine superbike. This bike is fitted with an aircraft grade jet engine, not a common engine choice for motorcycle manufacturers.

Suspension and Steering

Front end

Motorcycle steering and suspension can be controlled by several different types of front end. 

The most common form, by far, is the telescopic fork which consists of sliding steel tubes with long springs inside which use hydraulic fluid for damping shock absorbers. The front fork is one of the most critical parts of a motorcycle. The angle of rake determines how controllable the steering is. The more horizontal the forks are the more laid back the handling, more vertical = more twitchy and agile.

Girder front ends can be found on the radicalConfederate Wraith motorcycle. The Wraith has an advanced 'multi-link' girder front end. One of the earliest types of motorcycle front suspension, the girder fork consists of a pair of uprights attached to the triple clamp by linkages with a spring usually between the top and bottom triple clamps.

Hub centre steering is characterized by horizontal forks running to the center of the front wheel where by a complicated series of pushrods the wheel is turned. Hub centre steering can be found on the The BimotaTesi 1D, Tesi 2D and Suzuki Nuda concept.

Steering dampers can be found on many modern sportbikes and all race bikes, steering dampers are similar to telescopic forks in that they provide a dampening effect to bumps in the road. A steering damper provides a resistive force against the direction of movement, giving a controlled compression and rebound. Dampers are velocity dependent so the faster the spring moves (like when you hit a bump), the more resistance the damper provides. If you attach a damper there will be a dampening force that will tend to stop any steering motion. In most cornering at mid to high speeds, your front wheel steers very little to lean you into a corner so the damper doesn't have much of an impact. However, if the wheel hits a groove and starts oscillating back and forth vigorously, the steering damper will resist the movement and dissipate the energy providing more stability to the whole bike. The level of dampening can be adjusted quickly and easily by way of a dial on most units.

Rear shocks

Rear shocks usually come in three different forms:

Dual shocks. One shock absorber placed either side of the wheel attached to the swingarm and frame.

Monoshocks. One shock positioned at the front of the swingarm, above the swingarm pivot bolt. This type of shock is found on most modern bikes, especially sportsbikes.

Transmissions

Manual transmission. Most bike transmissions are manual sequential gearboxes, with neutral positioned between first and second. After second gear each gear can only be used in order. Reverse is only fitted to the largest touring bikes like the Honda GoldWing.

Automatic transmissions can be found in many scooters and some touring bikes.

Chain drive is the most common form of transmission to get power from the gearbox to the rear wheel. Chains require regular maintenance and lubrication. They also require periodical adjustment and change because of the stretching incurred over time.

Shaft drive is found on many touring bikes and BMW uses them on many of their models. Shaft drive units are completely enclosed and almost maintenance free, quiet and clean. Shaft drives drain power from the engine because of the complicated gearing required, they are also heavier than chains or belts.

Belt drive is found on many Buell bikes among others. Belts are quiet, clean and efficient although they do stretch over time like a chain. Belts are limited in the amount of power they can handle.

Exhausts

The position of a motorcycle's exhaust can effect the bikes characteristics, especially on high speed sportsbikes. Underseat exhausts, a Ducati favorite since the famous 916, were developed to reduce windresistance by putting them up out of the airflow - good. As a by product it raises the bikes center of gravity - not good. The traditional position of exhausts, either side of the rear wheel has its advantages and disadvantages too. First of all they are not the best looking pieces of kit and can clutter up the appearance, they can also disrupt airflow and ground clearance can be in issue. But if they are positioned low they can help lower the center of gravity, they free up underseat space for storage and the engineering is thoroughly researched.

Aftermarket performance exhausts can expel exhaust fumes faster permitting a longer power stroke. However, many modern production bikes already have a tuned system and an expensive performance exhaust may only operate effectively at a narrower rpm range. Louder, and often illegal, some belive that performance exhausts are safer as they can warn people who may have failed to see the bike.