Zündapp Janus was the name of a microcar model made by Zündapp, as well as the as the only car ever made by Zundapp. in Germany between 1957 and 1958. Originally Zündapp made motorcycles, but in 1954 decided to make a more weatherproof vehicle. They looked at designs from Kroboth, Brütsch, and Fuldamobil before settling for a design by Dornier Flugzeugwerke. The novel design featured a front-opening door for access to the front seat, as well as a rear-opening door for access to the rear-facing rear seat; this "coming or going" design was given the name of the Roman god, Janus, usually pictured having two faces: one looks forward while the other one looks back. The car was powered by a mid-mounted 2-stroke single cylinder 245 cc (15 cubic inch displacement) engine unique to the Janus developing 14 hp (10 kW), enabling a top speed of 80 km/h (50 mph). The suspension was of the MacPherson strut type that proved to be very comfortable. Production started in June 1957, but only 1731 cars were made in the first six months. By mid-1958, Zündapp abandoned the project and sold the factory to Bosch. A total of 6902 Zündapp Janus cars were made.
While in racing and sports cars the mid-engine configuration leads to optimal car handling, acceleration and braking, the engine was much lighter than the rear passengers, leading to a variable center of gravity.
In the movie Cars 2, the villainous character Professor Z is a Zündapp Janus. This was done so to avoid any legal battles with companies angry at their products being portrayed as evil.
Kleinwagen, Small Cars, Petites Voitures, by Benedikt Taschen, 1994