I had a set custom made way back in the day. Lathe turned aluminum, perfectly smooth and concentric. So perfect that it was actually kind of annoying, as I never found a tire round enough that I couldn't detect imperfection in it. Nothing like riding on $400 worth of tires and thinking "Man, I can so feel that lump near the valve stem". They also were heavy, and didn't fold. So eventually I bought a pair of Performance ones for traveling to races...