The all-carbon wheels on the Koenigsegg Agera R are so light, you can toss them into the air and catch them.
It's actually very nice that Koenigsegg gave this demonstration of the weight of these hollow carbon wheels, because they have no quoted technical specs. We don't know how much they weigh precisely, only that they save nearly 5kg per wheel compared to an unquoted normal wheel.
Maybe Christian "Bond Villain" von Koenigsegg will give us an answer on the upcoming season of Inside Koenigsegg.
(Hat tip to Hermann!)