According to everything I’ve read; UDH hangers are supposed to absorb impact by rotating, but I’ve seen a bunch of Trek Rail pics with the derailleur sheared in two, broken spokes and destroyed seat-stays after the hanger rotated backwards allowing the jockey wheels to contact the cassette.
So what does this designed rotation actually achieve?

Generates revenue for SRAM.

 

Mission accomplished

 

I've witnessed one crash where the UDH rotated and did exactly what it was supposed to do. It looked nasty, but pulling the wheel and a few minutes with a multi tool and the bike was ready to go. I was impressed.

Also, if it saves having to special order one from the hundreds of separate designs when a customer comes in with a broken hanger, then it's done its job. I keep a few UDH's in stock, doing the same with the separate designs would have a lot tied up in inventory.

 

I didn't know it rotated? I'm all for universal. It should have happened a long time ago. That said, my opinion is to make hangers robust and the frame interface more robust. With both those things issues are few and far between and straighten a thick hanger is easier and more reliable. Any flex tricks could cause more issues than they solve. Flex should come from the mech. Flex in the hanger and mech sounds like a good way to end up in the spokes.

 

I finished building a bicycle earlier this winter and had it designed for a UDH and I like it. The dropout is simple as far as the machining and the UDH fits very secure and does what it is supposed to do without issue.

As far as it twisting away during a crash, I think that will only happen in a small percentage of derailleur damaging crashes. You'd have to have a hard hit in just the right way to have the UDH spin and not destroy the derailleur or hanger. But, I suppose even having it work once in every 10 derailleur-killing crashes is better than zero.

As far as the license, SRAM offers the UDH license for free making adoption by frame manufacturers more likely. With their new direct mount derailleurs on the way, it seems like the UDH standard was as much of a way to get bike manufacturers to adopt a dropout that could be used with the DM derailleur. If they had announced the DM before the UDH, nobody would have bought them as it would have taken a special SRAM-specific dropout that wasn't on any (or many) bikes. By creating the UDH and licensing it for free, they got a bunch of bike manufacturers to adopt the standard which they can now leverage into DM derailleur sales while keeping the option of non-DM derailleurs. Pretty savvy.

However, to me that doesn't diminish the advantages of having somewhat standardized derailleur hangar that is nicely designed and executes its, albeit simple, function well.

 

I'm not sure you could call UDH a good design when it CAUSES this sort of carnage, and perversely, doesn't break in the process which is the primary protection role of a hanger... (the damage in these pics wasn't caused by crashes; it was caused by the UDH hanger rotating).

 

Is this only happening on the Trek Rail? I have not seen any other posts about this problem yet. Maybe a design issue with the frame/hanger interface?

 

I don’t see why it can’t happen with other bikes, unless Trek have screwed up the implementation.
As long as the hanger can rotate sufficiently to allow the derailleur to get pulled into the cluster it can happen on any UDH bike…

 

I’ve not long got a 2022 Chameleon and at first I was pleased that it had a UDH. Then started looking into the issues like the frame damage.

However everything I could find was on Treks. Along with Treks snapping the UHD bolt whilst torquing to spec. Seems like a Trek issue.

 

Interesting. Just yesterday I was looking at the pictures of SRAM's new derailleur and was wondering how it would work with Split Pivot suspension. Apparently not too well. There is much less material to support the hanger than in case of ordinary dropouts.

 

Just had my Pivot Firebird UDH crunch the derailleur and do some minor damage to the stay. The derailure just rotates and smashes into the frame. Bad design.

 

This is a very interesting discussion.....with pictures.....about UDH. Just want to ask though, it's not the UDH that's rotating and breaking the frame, it's the RD, right?