My simplistic belief is their spokes have some kind of sealed, stretchable bladder inside that expands under vacuum and stays in there

I was thinking exactly the same thing! or some heat-expanding foam cores

Matthieu Libeert
Founder MAT2 Composites X Sports
website: www.mat2composites.com

I doubt they leave them in there though. Even if the bladders or whatever they are using only weighed 50 grams, these are $50,000 wheels designed specifically to be as lightweight as possible. Not to mentioned the efforts they go through to balance each wheel perfectly to travel at 450kph, I don't believe it would be possible to achieve this while leaving any more material than necessary inside.

I do believe they sandwich the cf between 2 milled parts of aluminum. I think that is how they get the nice finish inside and out. If you look when they remove the barrel off of the barrel form you can see what looks like the negative of the spoke. I could be wrong too

wouldn't be strong enough to hold a car if they didn't use any cores or something I think

Matthieu Libeert
Founder MAT2 Composites X Sports
website: www.mat2composites.com