nice breakdown donp!

i started to step into a model of it... but i'd be lost down that path for days - so i stepped away from the temptation and went back to looking at pictures of bicycles on the internet... (while trying to get some work done...)

wondering about the tension ring. i don't think the point load transfers out the length of the rafter - rather it would want to roll the rafter and try to slide down its mate, before pushing straight out - twisting the entire structure perhaps?

obvious in your example that it is not needed in a straight down load, and add some shear planes to it (sheathing, boards, something) and it starts to become a very stout structure.

check out that first link - there are some geometry calcs in there for getting to optimal member sizing vs. number of spokes.