Two Convertibles with some similarities, but otherwise different in most aspects such as the modifications, starting price, horsepower, height, fuel economy, ground shadow size, and maximum occupancy. First of all, the 2018 BMW 2 Series Convertible M240i is priced $15,850 lower compared to the base MSRP of the 2018 Alfa Romeo 4C Spider. Also, the 2018 2 Series Convertible M240i has a more powerful engine than the 2018 4C Spider, and it gets 4 fewer miles on a gallon of fuel. In addition, the 4C Spider is both slightly smaller and significantly shorter than the 2 Series Convertible M240i. And then, the BMW 2 Series Convertible M240i seats two more passengers than the Alfa Romeo 4C Spider. Among similarities are the body structure and market segment.