Motorcycles are cheap to run, exciting to ride and a quick way to travel through traffic. Styles of motorcycles vary depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.In many parts of the world, motorcycles are among the least expensive and most widespread forms of motorised transport. After the Second World War, the BSA Group became the largest producer of motorcycles in the world, producing up to 75,000 bikes a year in the 1950s.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. Liquid-cooled motorcycles have a radiator (exactly like the radiator on a car) which is the primary way their heat is dispersed. Liquid cooled motorcycles have the potential for greater power at a given displacement, tighter tolerances, and longer operating life, whereas air cooled motorcycles are potentially cheaper to purchase, less mechanically complex and lighter weight.Only the largest touring motorcycles and a few models that are routinely used with a sidecar or converted to tricycle configuration are fitted with a reverse gear. At one time, motorcycles all used spoke wheels built up from separate components , but, except for dirtbikes, one-piece wheels are more common now. Brakes can either be drum or disc based, with disc brakes being more common on large, modern or more expensive motorcycles for their far superior stopping power, particularly in wet conditions.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. As can be seen from the streamlined appearance of new performance motorcycles, there is much aerodynamic technology included in the design. Modern fairings on touring and sport-touring motorcycles dramatically improve a rider’s comfort and attention on long rides by reducing the effect of the wind and rain on the body.While the reasons for people choosing to ride motorcycles are many and varied, those reasons are increasingly practical, with riders opting for a powered two-wheeler as a cost-efficient alternative to infrequent and expensive public transport systems, or as a means of avoiding or reducing the effects of urban congestion.Motorcycles from a number of manufacturers now have electric windshields, which raise and lower the windshield with the push of a button to the optimum height for conditions.In England, motorcycles are exempt from the £8 per day London congestion charge other vehicles have to pay to enter the city during the day.In many cultures, motorcycles are the primary means of motorized transport.Electric motorcycles are emission free during operation, producing the electricity that charges the batteries in them can be a cause of pollution. Street customs: Highly customised motorcycles with wild paint jobs also built for show, but constructed from a sport bike frame instead of a cruiser-style frame.The chassis (or frame) of a motorcycle is typically made from welded aluminum or steel (or alloy) struts, with the rear suspension being an integral component in the design.