Once upon a time, there were motorcycles, do-it-all machines with two wheels, a frame, a gas tank and an engine. Those days are long gone! Now we have all kinds of machines, specialized for different competitive, professional and leisure activities. Here are the most common ones you'll see out on the road, track and trail. Note: power (at the rear wheel) and weight numbers (with the motorcycle fuelled up and ready to ride, without rider or luggage) are broad estimates to give you a rough idea of these machines' capabilities and sizes.