According to
this article, prior to 1963, "California kids had started to take old 20-inch bicycles and customize them into motorcycle looking sport bikes. They were replacing the factory seats and handlebars and using instead 'Solo Polo' or 'banana' seats and tall 'butterfly' type bars. This California fad was noticed by Al Fritz the director of research and development for Schwinn, and he reacted very quickly, making a prototype that was mostly laughed at by the Schwinn upper management."