Two Convertibles with some similarities, but otherwise different in most aspects such as the starting price, horsepower, fuel economy, ground shadow size, height, and maximum occupancy. First of all, there is a notable difference in the starting price of the 2018 Alfa Romeo 4C Spider, which is $20,800 less than the base MSRP of the 2018 BMW 6 Series. Also, the 2018 6 Series has a more powerful engine than the 2018 4C Spider, and it gets 7 fewer miles on a gallon of fuel. In addition, not only 4C Spider is significantly smaller, but it's also slightly shorter than the 6 Series. And finally, you'll seat two more passengers in the BMW 6 Series than in the Alfa Romeo 4C Spider. Among similarities are the body structure and market segment.