I’m not familiar with those dropouts, but a quick Google image search tells me it may be possible to design a replacement insert that could accomodate a Transmission derailleur. It will ultimately depend on whether the frame may interfere with the clearance space required by the UDH spec from SRAM.
Unfortunately I can’t determne that from the photos of the inserts alone.
Thank you for reply. I have a frame and two sets of g1 dropouts. Interferention with the frame is slightly relaxed, as I can move the axle slightly back, increasing chainstay length (but in this case I must also make a new left dropout). My problem - I cannot found g1 specs and I am not familiar with 3d modeling software to make at least POC on kinda 3d printer…
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So what you’ll need is a drop out that bolts to the outside face and steps in a little. There is a 7mm gap between the axle end and the frame end in the UDH specs which has a 20mm hole and is 12.7mm thick. It looks like its possible to do. One of the guys local to you should be able to gelp you model it out etc.
Hm. May be your Idea with flipping mount side is good. Still not sure if I found somebody to help me and which material should I use. From the inside it looks so:
There are a few things to consider too. Transmission is Thru axle only. Im gyessing 26" is QR and 135 spacing. Minimum youll need is 142 axle length. So youll have to do some measuring to see if you can fit a 142 hub in and the disc miss the frame. Then you could look at seeing if a modified left side frame end can be used on the right side. Maybe with some shims or material removed and the center bored out.
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As you can see on photos it’s 142 thru axle
Ahhh, wasn’t sure if that was yours or a google pic. I reckon youll go real close with a left hand end modified for the right side. Good luck. 
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Оr as an Idea, just to use paragon CLDR2073 dropouts and model the mounts just from flat steel plates? To slightly move the wheel axle is a less problem that errors in orifice positioning. So then I must just to know positions of frame mount holes and to model 4 (similar) mount plates, laser cut them somewhere from 1mm stainless steel and to weld in place? I am able to tig weld myself.
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So, after many (many) months (years?) of lurking around here, I think I’ve finally got a small tidbit to contribute to the greater knowledge of the framebuilding community. That said, maybe this is an already well known issue and I’m just adding to the noise. Or, I could just be missing something? Anyway, dissertation commencing:
I’ve spent the last several months trying to get myself up to speed with CAD (Fusion) and, specifically, working on a dropout design to use on some frames of mine. Since UDH seems to be sticking around, that’s what I figured I’d build around. I’m very close to the final iteration of my design, and have sprung for a GX Transmission derailleur to have on hand while I test final plastic 3D prints. All seemed well and hunky-dory. But, I just happened to be visiting some shop buddies last week with the prototype prints and we bolted up a XX Transmission derailleur and gasp it doesn’t fit the same as the GX.
For some context, this is a hooded design meant to be used with 22.2 straight stays. I’m using the rev. ‘H’ UDH docs and 3D mask for the design, so should be up to date, or so says the UDH website. The only violation of the mask is at the seat stay hood, where the chainline is intended for idler pulleys (not my application). Otherwise, according to the CAD mask, the design is free and clear and should be compatible with any Transmission derailleur.
The issue appears to be the outer ‘arm’ of the co-axial mount on the XX version. It extends roughly 5.8-6mm further forward than the GX version, at least where it intersects with my design. What this means is that there is a gap between the inner arm and the designated forward stop on the inner side of the dropout. With the XX der, the outer arm contacts the outer hood of the dropout before contacting the actual, dedicated forward stop on the inner side. The images show the interference better than my description.
OR: maybe I’m just missing something. I’ve gone round and round in my head, in Fusion, at the shop with the actual prints and derailleurs in hand. I can’t see what I might be doing wrong. The GX is good, the XX isn’t. But, I might have just looked at all of this so long that I can’t see the issue staring me in the face?
What does all this mean? I don’t know. Seems like a pretty big issue if one was to build a gagillion dollar custom bike for a customer, only to find their $650 derailleur is banging into their brand new frame. Cthulhu forbid, said expensive frame also had a wicked expensive paint job. The chips! Think of the chips! Anyway, makes the builder look a little silly/inept, when in reality the billion dollar corporation doesn’t appear to have their engineering revisions under control. I’m modifying my design so that it’ll clear the XX derailleur, but it seems crazy to have the official documentation (seemingly) not match up with the products on the ground.
Thoughts? Feelings? Experiences?
My only thought is that having seeing the installation process of these derailleurs (not owning one myself) the rotational stop isn’t actually used by the transmission derailleurs. I don’t know if they would still be contacting your dropouts once installed properly. But I think that has to do with chain length.
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Yeah, this is definitely more of a concern with a chain that is getting close to the short end of the spectrum, and/or a derailleur swinging around before it’s tightened down. It’s certainly a little bit of a fringe concern, but it’s bummer that it’s whanging into the dropout. Given what I do for the day job, chips are the bane of my existence. I’ve had folks come to me beyond distraught that their new frame got it’s first chip, and it would be a stinker to have that first chip be because of a funky dimension variance between two versions of Transmission derailleurs. Feels like it’d be nice if the first thing the derailleur contacted was the in-built forward stop, rather than some other part of the structure.
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@fluxcustoms Thanks for sharing that. I didn’t realize the XX and GX were slightly different.
I believe this is the case. I can’t speak for all combinations of derailleurs, chainstay lengths, chain lengths, and frames, but for the two Transmission bikes I set up, the derailleur is nowhere near hitting the stop of the dropout.
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I can confirm this is also the case for my XO transmission-equipped bike.
I can confirm what @Daniel_Y and @liberationfab commented, my XX transmission derailleur is not close to the rotational stop. The length of the chain determines the position of the derailleur; the stop is there for use with the UDH.
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So, I guess my beef is this: since the adjustment of the Transmission derailleur is based on chain length, which is in turn based on a calculation given by Sram, based on a given chainstay length, down to the millimeter, I would make the assumption that they (Sram) are assuming that the derailleur has full movement on the dropout, forward and back according their specs, to accommodate the prescribed chain length.
In the case of the XX derailleur, it wouldn’t have the full range of motion, and if say the chain length prescribed is on the shorter end (i.e. closer to the forward stop of the dropout), then I can envision a scenario where an end user cuts the chain to the length directed by Sram, only to find that the XX derailleur doesn’t have enough forward rotation to actually connect the chain because it is contacting, in my case, the hood of the dropout, rather than the Sram specified forward UDH stop. Kind of a bummer on a $150 chain to cut it short and have to run multiple quick links, or buy a new chain. Or, bigger bummer: run it short and potentially have the derailleur bind when shifting into the 52t. But maybe it’d just (quite forcibly) rotate itself forward in the dropout in that instance?
The only reason I might be (likely am) making a mountain out of a molehill, is that the derailleur probably has more than enough movement in the cage to accommodate a chain that is a bit on the short side. And they’re calculating on the conservative side I’m assuming (right…right?). It’s designed to go on full suspensions with substantial movement of the chain through the travel range after all. In the setup, you’re locking the cage for the adjustment, then releasing it to let the cage give the chain tension, so it’s got some in-built fudge-factor for chain length. There’s just a whole lot of assumptions in all that, and I don’t know what sort of allowance Sram makes for this, and it bugs the ever living hell out of me!
Ok. Rant over. I promise I’m not nearly as hysterical as I sound.
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I just cut a $30 SLX chain too short, and it almost financially ruined me. I can’t imagine a $150 chain!
I agree, it’s weird that they create a rotational stop but don’t use it. Most bikes I have seen with the proper length chain have the derailleur clocked quite far back. At first I thought it was a mistake, but I guess that is just how it goes:
What I am worried about (actually, I don’t really worry since I don’t use UDH) is what will the alleged gravel and road transmission will look like. Many of the features of the mountain transmission (2.5mm offset, full suspension, impact strength, shifting under torque) are not important for road/gravel. Will they invent a new spec? Will they pivot away from transmission? Will the dropouts be incompatible? No one knows…
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The frame interface ie. 20mm hole is here to stay in my opinion. It suits carbon way better than the previous methos ie. bolted on hanger. My bet is Shimanos ders’ will bolt up to this interface as well. SRAM also won’t worry about the forward swing of the body in the same vane, carbon uses a straight sided stay into the frame end, so nothing to hit. Metal frame designers/builders just have to design around that.
I’m pretty sure the frame interface and UDH hanger will not change. So much work put into launching the standard, engineering products around it and getting a pretty good uptake from other brands. And not only MTB brands either.
I had a chat to a SRAM rep. quite a while ago (probably 2 years or so) about the differences between road & MTB hanger specs and how UDH would work with a road derailleur. The answer I got was that the engineers (at SRAM) were evaluating whether they would make a separate road hanger. That does not seem to have been necessary. At least not for SRAM derailleurs.
Prova Cyles has been using the UDH interface for quite a while and I know that at some point they were getting custom hangers made that conform to road spec. I’m not sure just how necessary that actually is, but a nice touch I suppose.
We actually had to redesign our UDH-compatible hooded dropout to account for the forward-swing. Our original design (not by me) had the front part of the hood inside the designated clearance space set out in the UDH CAD files. Haven’t had an issue with transmission setups on that particular dropout so far, but I suspect there are some chainring/chainstay length combos that may be problematic. I even went to the trouble to make a chart predicting which combos may cause interference.
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After speaking with Mark @ Prova 2 years ago after the show in the pub, he explained what was going on from his information directly from SRAM. It’s why I have dived 100% in on using the frame interface. Ian @ Lost also told me they had some issues with a road der on the mtb UDH hanger and they traced it back to the hanger geo and hence why Mark ordered the road spec UDH hangers.
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Care to elaborate on what issues he had with UDH and road derailleurs? Only “issue” that I found is that Sram road AXS derailleurs look like they are hanging a bit akwardly with the battery down. Set up correctly and shifts perfectly but looks a bit weird. I thought I did something wrong so contacted one of the Sram guys that worked on the UDH/Transmission design but it seems to be a “feature” but not one they are very proud of. 
But I would love to know if Prova fixed this issue with a modified UDH hanger.
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