Answer: BMW Isetta

Microcars are a fascinating bit of automotive history. Compared to their much larger brethren, microcars were extremely tiny and shared some common traits: they tended to be under six feet wide, around seven feet long, only seated one or two people (small framed people at that), had a three wheel reverse-tricycle footprint (some models had a four wheel setup to reduce roll-over accidents), and typically a single cylinder engine that had more in common with a motorcycle engine than the beefy engines that dominated mid-20th century car design.

Among all the microcars that popped up between the 1940s and the 1960s, the single best selling single-cylinder model of all time was the BMW Isetta. Although the Isetta was produced by different companies in different countries (the design originated in the 1950s in Italy when the Iso SpA firm, a company then known for refrigerators, motor scooters, and small three-wheeled trucks branched out into tiny cars), it was the BMW version that combined the right features to gain mass appeal. The biggest selling point of the BMW redesign was a powerful (for its size) motorcycle engine inside the Isetta that could generate 13HP and had a fuel efficiency of 78 miles per gallon (U.S.).

Between 1955 and 1962, BMW built 161,728 of the tiny cars before ceasing production, three years after the 1959 introduction of the conventionally modern-looking BMW 700—an economy car with a 2 cylinder 697cc engine and styling less like a bubble-shaped toy car and more like other two-door compact cars of the day.