Once upon a way back when, a few scant patent drawings of a Harley-Davidson leaning trike made their way to the web. Apparently, the company went so far as to produce a few prototypes under the codename Penster. The trikes were penned by none other than legendary custom car builder John Buttera, and despite the inherent awkwardness of the trike design, the Penster looks pretty good. For reasons that remain unclear, the design was never given the go-ahead for production. Instead, Harley buyers with a heart for three wheels wound up with the Tri-Glide.
Not surprisingly, the Penster makes use of a 45-degree air-cooled V-Twin for its propulsion, though details on exactly how the leaning mechanism works are still scant. These prototypes were hewn in 2006 and now reside in the Harley-Davidson museum. They stand out as an impressive piece of forward thinking from a company that holds steadfast to its traditions.