If anything is proof of the cyclical nature of design and taste, the 1985 Frog Design FZ750 Concept, penned by the firm's founder Hartmut Esslinger for Yamaha, is a great example. The bike's styling and color scheme is incredibly dated. Yet time has been kind to the design, which has great proportions and a sleek, geometric style that still seems futuristic despite its clear early 1980s provenance.
The original prototype was created for Yamaha and was never produced, but Honda saw the published design and used it as inspiration for their Hurricane sport bike. The prototype is now entering SFMOMA's permanent collection. More info at Frog's blog HERE.