Two Convertibles, but completely different in all significant aspects: model year, modifications, horsepower, height, starting price, fuel economy, ground shadow size, and maximum occupancy. First of all, there is a notable difference in the starting price of the 2021 BMW M240i Convertible, which is $14,950 less than the base MSRP of the 2018 Alfa Romeo 4C Spider, which is three model years older. Also, the 2021 M240i Convertible has a more powerful engine and gets 4 mpg less than the 2018 4C Spider. In addition, the 4C Spider is both slightly smaller and significantly shorter than the M240i Convertible. And then, the BMW M240i Convertible seats two more passengers than the Alfa Romeo 4C Spider. Among similarities are the body structure and market segment.