Construction

Construction
VariationsVariations exist:
There are two basic forms of motorcycles: offroad and street. Some motorcycles have floorboards instead of footpegs. Some motorcycles can be fitted with a sidecar, this converting it into a 3-wheeler or "hack". There are other 3-wheeled variations, commonly referred to as a trike or motortricycle. Motorcycle manufacturers often also produce All-terrain vehicles or ATVs. These have two or more back wheels, usually two front wheels, an open driver's seat and a motorcycle-type handlebar. (Early models had a single front wheel, but these were prone to rollovers.) ATVs are used off-road for utility and recreation. However, a proper motorcycle has fewer than four wheels in contact with the ground.
ChassisThe 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 is 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.
The fuel tank is usually mounted above the engine. This tank is generally made of stamped, brazed or welded sheet metal, or blow molded high-density polyethylene. At least one motorcycle manufacturer (Buell) offer models that use a hollow frame as the fuel tank, and various manufacturers offer designs which use part of the frame as an oil reservoir. The wheel rims are usually steel (generally with steel spokes and an aluminium hub) or 'mag' type cast or machined aluminum. Performance racing motorcycles often use carbon-fiber wheels, but the expense of these wheels is prohibitively high for general usage.
A plastic or fiberglass shell, known as a fairing, is placed over the frame in 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 horsepower 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, but unfortunately no one has been able to overcome the effect from the turbulence caused by the spinning front wheel which disallows the motorcycle from cutting a clean path through the air. Another problem is 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. 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.