teleguy57 wrote:Not sure I understand the comment about pulling Us into Vs or vice versa....?
When you tension the spokes, you're essentially pulling the spoke bed down from the brake track. A "V" shape is very well equipped to handle that since that is the shape that the loads would naturally take from the brake track to the spoke bed. A "U" shape requires more support to maintain the "U" shape. Tie a rope between two fixed points, where the rope has plenty of slack to hang down. Unloaded, the rope might naturally be happy to hang in a "U" shape. Clip a small weight to the rope and it will instantly assume a "V" shape. A "V" shape is naturally aligned with the spoke loads, where a "U" shape isn't. You need to add material, and therefore weight, to support the "U."
I would be very skeptical of "U" shaped rims that are much lighter than what you see from the majors. Our target for a 52mm rim is 480g. We might get a little under that, but not much. I've run the weight vs aero drag iterations through the analyticicycling.com calculator six ways from Sunday and the amount of aero gain our Rail rim has shown handily beats the minor weight penalty over lighter, more "V" shaped rims, in everything short of a TT up Alpe d'Huez. In that case you'd be using a whole different type of wheel anyhow.