One of the reasons Lexus built its own top (and the IS C looks a little heavy in the rear) is the insistence from the engineers on a useful amount of cargo capacity. When the top is up, there are 10.8 cubic feet of space (or two golf bags, which is the standard of measure in the adult world), and when the top is down there's 2.4 cubic feet of cargo capacity (or one golf bag). This is more than a BMW 3 Series convertible, a good comparison since the IS C has a full-size spare tire while the 3 Series has no spare tire at all because it uses run-flat tires.