"Split Hub Center Steering" is what I call the system used in the racer's steered rear suspension. A wing bearing universal joint connects the left side drive hub to the right side steering hub. Rear steering is 34% of the front, and in the same direction.
Yes, steering geometry matters at the rear wheel as much as the front. A LOT of work was done to determine which geometry works and which doesn't. Instability from weaves, and speed wobbles with just the rear wheel, is no fun. That hasn't happened to this bike, but has happened with the electric one.
The drum brake rear wheel from the EX500 worked very well for this experiment. It is red because the donor bike came with a parts bike that had red wheels - no clever or creative aesthetics involved. The wheel was sent to Kosman Specialties to have the hub bored out back in 2009. That was the only machine work for this project that I didn't perform, since the wheel didn't fit in my lathe/mill.
The rest of the machined parts came out of my Grizzly G0516 lathe/mill. I got a lot of good parts out of that machine, but it has since been sold. The next racer will need more serious machinery located in a serious shop, rather than my kitchen (Seriously!).