First, don't believe the hype
First, don't believe the hype. Alloy wheels are not necessarily lighter than steel. In this case, the alloys are larger, so the mass is lower with the steel wheels and covers. The tires also matter and the ones with the better fuel economy will be harder, and have less rolling resistance. The Prius wheels/tires always have been chosen carefully for maximum fuel economy. The BMW i3 takes this to almost comical extremes.