I believe SRAM will eventually only sell UDH derailleurs. That we have a hanger to use for other brands means that if a frame builder or manufacturer builds UDH frames they can still spec what ever drivetrain they want. They just need to make a road hanger for it. All the carbon production bikes will be built with UDH as it is easier to mould in carbon than for the usual style of hanger and much stronger so less frame failures.
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Im not fussed. Ive munched 3 derailleurs in 30 years of riding mtb. I think it over complicates the whole system. Id just as happily go back to 11 speed and be done with it.
Its the same with the guys at Trinity with their mid mounted cassette system. Over complicated and way too much drag on the drivetrain. I started modelling a similar setup some 10 years ago and shelved it for those reasons.
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Itâs not a massive performance advantage by any means, itâs just going to be adopted by everyone. So maybe itâs more analogous to thru axles or 1x drivetrains. Neither of those things revolutionized mountain bikes but itâs hard to buy a new bike without them.
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If manufacturers decide build frames for the coaxial derailleur, then the UDH itself will become irrelevant. It will be the interface that the UDH is compatible with that matters. At that point people will be able to design unique derailleur hangers that are UDH interface compatible. The UDH will probably remain the primary hanger for the UDH interface, but not necessarily the only one. SRAMâs plan to replace legacy derailleurs with coaxial derailleurs may ultimately fail. Ironically, itâs coaxial derailleur interface may endure, without the coaxial derailleur that it was intended for.
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I think the moniker UDH is what most people are using to refer to the coaxial interface. Its the interface we are concerned with. If you are a literal person it will probably trigger you, but Im seeing lots of people here and across the bike world refering to the hole in the frame as the UDH standard. Similar to how clipless pedals are refered to by a lot of people.
The hanger itself is seen by many as the undesirable aspect of UDH. This is due primarily to itâs excessive width(requiring a similarly wide support on the non drive side). People can work with the UDH as an interface(several attractive UDH dropouts have been presented recently). The ungainly hanger with itâs protruding fin are problematic. On that issue, I should mention that the fin and rotation stop features are NOT required by SRAM to be UDH compliant. They are merely recommended.
Agreed, there is a fair bit of bulk in that set up with the hanger and then what will be the axle receiver. The hanger or the axle receiver is an integral part of the UDH/coaxial setup though and the fin is there, in part, to protect âsoftâ carbon frames from chain drop. Though I notice in this pic the axle receiver doesnât have the fin on it so maybe itâs a hanger only thing purely for the pivot stop.
There are definitely ways to build around the specification and maybe if builders want to adopt it, they move away froma hooded drop out or use the ones that are already available. A bit of lateral thinking can work here. Itâs why I went back to the plate style and also figured out a layout that means the NDS frame end doesnât have the 7mm extra on it either. 
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A remarkable coincidence! Long Sheng has a new UDH dropout design that looks like it was inspired by the examples posted in this
discussion.
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Itâs a recent addition to their product line. There is also a flat mount version. No doubt the cost will be competitive.
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For those folks that have been working with UDH for a bit now, what are you doing for your dummy axles in your jigs?
I havenât built with UDH yet, but I was planning to buy an all aluminum hanger to use only for framebuilding. That way a regular dummy axle would work.
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We had to make an adapter for our UDH flat mount dropouts. it was much more cost-effective than to create an entirely new dummy axle.
https://www.instagram.com/p/CjIlpFXrzse/?utm_source=ig_web_copy_link
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I just made a round plug, similar to PMW and use that with the normal 142/148 dummy axle. Leave it short in the bore of the dropout so that the bolt can pull it all up tight.
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Based on this Instagram post, it seems like coaxial is here.
https://www.instagram.com/p/Cp55xMvyFUQ/?igshid=MDJmNzVkMjY=
The moment we feared/been waiting for has come!
Review: SRAM XX SL Eagle review: A new frontier for the rear derailleur - Escape Collective
Development Story: Development Story: SRAM's New Eagle Transmission - Pinkbike
According to the review, it seems like the rigid derailleur and connection is a big jump up in shift performance.
From the custom framebuilder perspective I have two thoughts:
Reading the articles and looking at the derailleur, the new groupsets apear to ignore the UDHâs fin. I wonder if we designed a dropout for a hanger with the fin chopped off, it would still be compatible with the new groupsets. The fin is what is killing a lot of the metal dropout designs.
$550 derailleurs, $400 cassettes, and $100 chains are crazy in my opinion. I would only be interested in designing a dropout if they released a lower-cost mechanical version.
For a sanity check:
| New XO1 | XT M8100 | |
|---|---|---|
| Derailleur | $550 | $122 |
| Shifter | $150 | $63 |
| Cassette | $400 | $165 |
| Chain | $100 | $49 |
| Total | $1,200 | $399 |
IMO, you are not bringing new people into the sport with these sorts of products. You are just milking the existing base for more money. Also, at scale, the environmental impact (materials, energy, resources) is often proportional to the cost of parts. So unless SRAM is playing games with the pricing (which they probably are), these parts consume a lot of resources to produce.
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It looks like the rearward impact rotation is built into the derailleur, making the dropout nub unnecessary. Hmm, that would allow us to make a more compact dropout.
I could see having a Sram Transmission specific dropout for the customers who plan to use it. It would mean that no other derailleur system would be compatible. For lots of people thatâs a non-starter. But for those that plan to stay within the Sram universe, it would be a slight advantage.
This video shows how the rearward impact position works.
The derailleur mount uses a âknurled ringâ that limits how far the derailleur can swing back. Thatâs probably why you have to cinch the mount down much tighter than a traditional derailleur.
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Good point. I feel like that nub and fin was one of those âyou know what would be coolâŚâ moments someone had 5 years ago when designing the UDH.
I can see our own standard: SUDH - Somewhat Universal Derailleur Hanger where we delete the nub and fin.
SUDH would be compatible with regular derailleurs and the current iteration of SRAMâs derailleur. We could manufacture hangers without a fin, or just sand it off a real UDH. The only problem with SUDH is that you couldnât guarantee that is compatible with all future drivetrains.
Itâs not ideal, but given that the current crop of UDH dropouts are ugly, since and no one can predict what SRAM and Shimano plan to do in the future, SUDH seems like a viable option.
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I donât know how to reply to specific things you said, but articles did say the cassette was shifter outboard 2.5mm.
In the comments in Oinkbike (typo but Iâm keeping it) Cotic mentioned that they had been burned by SRAM updating the UDH spec and they have bikes now incompatible with the new system. Just a few things to keep in mind if designing a dropout.
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Ah, I totally missed that. That makes total sense. The fat UDH fin was just a trojan horse for 55mm chainlines! Well, that sucks. there goes any hope for a UDH modification.
I love Coticâs no BS comment:
@mikekazimer: Itâs worth losing sleep over when itâs not backwards compatible with any other SRAM drivetrain, and actually not backwards compatible with every UDH frame. We designed some new dropouts to Revision E of UDH a couple of years ago with structure on the dropout face plane, like we always have, like a lot of bikes do, then because SRAM canât control their data dissemination properly, we find out 6 months ago that weâre now at Revision G, there a cassette and a chain right where I have frame structure and our bikes wonât be Transmission compatible despite being UDH. I am betting we wonât be the only brand with this issue.
This is my takeaway: Iâll just let SRAM play its games with its $2k electronic groupsets 
. I will stick with the beautiful Paragon DR1065 for my designs!
Highlight the text > Quote
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