Racing motorcycles are specially designed for closed circuit tracks or road racing. Most motorcycles designed for road courses have fiberglass or carbon fiber fairings around the front and engine to improve aerodynamics. They have stiff suspension systems to improve handling agility on curves, and their engines are modified to produce more power. In Europe, two-person racing cycles with sidecars are popular.
Motorcycles used for drag racing are often lengthened to improve high-speed handling stability. Bars extend behind the rear wheel to prevent the front wheel from lifting off the ground during acceleration, which would cause the cycle to flip over. A wide rear tire with no tread maximizes tire contact with the track surface. In some types of motorcycle racing, alcohol or nitromethane fuel may be used instead of gasoline to boost power. Many racing motorcycles can reach speeds as high as 390 km/h (242 mph) from a standing start in a quarter mile.