If one adds a carbon cover of weight x kg to a wheel of y kg, the total weight is x+y kg which is greater than y kg. Unless of course the cover is negative x kg.
But the average density of the physical stuff ( wheel plus cover) is less than that of the wheel alone, so it's lighter
I It is... this was during the Ducati open day at Rykas right... or very close to it. We were all under the impression it was a real SL. Obviously not
The cover is there to do a job. You're knowingly sacrificing what little weight penalty there is because the advantage it gives far outweighs it. No different in concept than the hubcaps on a formula1 car. He however won't be going fast enough to ever take advantage of it.