Since the days of $4 gas began, the single-cylinder motorcycles and scooters that dominate international megacities have become increasingly common on American streets. Engineers at Yamaha created the Y125 Moegi concept to capitalize on that trend. They based it on the company's first motorcycle, the 1955 125-cc YA-1, but they also included some modern touches, in particular an ultralight frame and a new cylinder design that could help make the Moegi one of the lightest and most fuel-efficient motorcycles ever.