Very cool! And you are totally right, this UDH debate is solely a titanium and steel problem 
A couple of good ideas and conversations between @mark_pmw @PineCycles @manzanitacycles
I agree with Mark that big manufacturers (like PMW) are in an awkward position that forces dropouts to be fully compliant with UDH, otherwise, they could be screwed
I also agree with Pine and Manzanita that a dropout that ignores UDH’s annoying features but is still compliant with (the current form) Transmission would make a much nicer dropout for metal bikes.
Potential solution?
This may sound stupid, but maybe the solution is to create a small Transmission only dropout, then a custom hanger (let’s call it NUDH) to adapt it back to regular drivetrains.
I only see two downsides to this approach:
- If SRAM changes its Transmission standard down the line, the dropout may not be compatible
- you end up with another hanger design out there
The fail state of problem 1 is that you just install the NUDH, which your bike is compatible with all other drivetrains for the foreseeable future. As per this thread: Shimano Direct Mount - #2 by project12 Shimano is likely to stick with regular derailleurs
And realistically, at the rate that the mainstream industry pumps out new standards, whatever we build will be “obsolete” in a few years.
Problem 2 is not really a problem, it is just the current precedent in our custom frame world. The only one true standard for us is whatever Paragon makes . And I never bought the “go to any bike shop and get a replacement hanger” argument. Carrying a spare hanger on your bike totally solves this problem.
Yes, all this sounds stupid, but I think this whole UDH exercise is pretty stupid . The fundamental problem is that we are designing the entire rear end of our bikes based on a derailleur hanger. It should be the other way around!
If you compare a “regular” hanger to UDH, the dropout needs to be much wider and the SS needs to be pushed outboard 5-6mm.
With road/gravel bikes, the wider NDS dropout can cause problems with the flat mount bosses. If you make the rear triangle symmetric, you will probably have to use FM160 to move the bosses away from the dropout.
With FM160, you have to use really long bosses (~1.5in [40mm]) to clear the chainstays
IMO, for metal road and gravel bikes, UDH and Transmission lead to a cascade of issues.