MattiThundrrr
Kona Fan
From the organizer of the coaster brake challenge where that bike was a competitor:How Bizarre, and what the hell are those on the rear hub?
"We have been exploring the many ways to keep one's hub cool. With grease, and with cooling fins etc. the best one thus far is a external water nozzle that one can spray the outside of the hub."
https://ratrodbikes.com/threads/coaster-brake-challenge-23.110036/