My take is the fin was there because the chain can fall off easily from 10 tooth sprockets when not adjusted correctly. Now with the narrow/wide teeth profile in the cassette sprockets and especially that 10 tooth and teh fact they have no limits screws is taht they don’t need the fin to look after dropped chains as it supposedly doesn’t happen anymore. That remains to be seen.
As I keep mentioning, the industry is geared towards standards for mass produced carbon, we, as a small community need to figure out ways around this to make those parts work on our frames. From what I can tell my drop out design already works with these derailleurs but I still need to grab the tech docs and sit down and have a look at it. Anyone persisting with hooded drops will have to figure out their own solution and archictecture. Depending on your business model and productions schedules this could mean designing and making your own parts or using the plug and play frames parts that will come from the great collaborations I am seeing here.
The rearward rotating after trail strike has always been a feature of the UDH so that part isn’t a new concept in these derailleurs. I am impressed with the strength of the system and the reported shifting robustness and speed means this is a real step up in drivetrains…sorry…transmissions.
To be honest as much as I am a Shimano fan boy I think Sram have done a really good job of raising the bar here. The fact you can replace damaged parts is a great step forward going back to having repairable products and unless you are a gram hunter and don’t mind your parts wearing out premamturely we’d all just go for the XO with alloy.
You’re right, but it appears there’s a difference between how it’s implemented with the hanger and the direct mount derailleur.
The hanger uses the fin to butt into a physical stop built into the dropout body to limit its rotation.
I believe the direct mount derailleur uses a “knurled ring” and a nub built into the derailleur to limit rotation. The knurled ring digs into the inner face of the dropout to provide the two stops.
If that’s the case, then it’s possible to design a dropout specifically for the Transmission derailleur. The dropout could likely be made a lot more compact. A win for steel frames at the expense of compatibility with every other derailleur on the market
I’m imagining a perfectly round dropout from readily available bar stock, maybe 31.8mm. @mark_pmw could produce them for much cheaper than something with an amorphous shape.
We’re working on it! I’m trying to source some documentation other than what’s already available. We don’t want to solve this puzzle with photos and animation just to shoot ourselves in the foot. We’ll continue to post new developments here. If we go out of spec for UDH, but come up with a better solution for steel bikes, it’s not a loss. We can always make a hanger that works with an optimized Transmissions dropout.
I whipped up a sketch using 1.25" bar stock as the outer diameter. It looks like there’s just enough room to clear the transmission derailleur. Based on the UDH drawings and help from an industry friend with one of the derailleurs on hand, I think it’ll work. It won’t be UDH compatible though.
I think we can safely throw UDH in the junkpile. It was just a place holder for Transmissions. I have a derailleur on the way, I’ll confirm fit and operation when I get it. As mentioned, we can make a hanger that will fit a dropout like this if needed.
I had a chance to sit down and research and understand the new Transmission stuff. After playing around with CAD, I realized the reason why I having so much trouble designing CNC dropouts for UDH: The dropouts have to accommodate both “regular” and SRAM’s new 2.5mm.
This is a draft UDH and SRAM design I played around with. I moved the slider to the outside of the dropouts. It works with UDH (which is pointless, because you can just replace the slider). Unfortunately, It is on the margin for compliance with the new drivetrains. It might work with plate sliders:
counter sunk screws might solve this, but those are easier to strip
chain hits the hooded dropout
not a problem with UDH and regular drivetrains
not a problem with “plate” style sliders
you need to offset the dropout 3mm lower to fit the UDH body
a matching NDS insert would need to be made
BB drop will be ~3mm higher
Opinion
The cost of the drivetrain, the batteries, non-backwards compatibility, and the disregard for fit (q factor) go against my design principles.
With 3D printing, I can hide the asymmetry by manipulating the SS and CS connection points. But I do not want to jack up prices by $500 for everyone (for printed dropouts) or compromise the aesthetics (with CNC dropouts) just so a few people can run a $2500 electronic drivetrain.
Nick and I built this bike last year with 3D-printed dropouts for UDH that are Transmission compatible:
If I wanted to design the latest and greatest bikes, I would be an engineer for Specialized and make carbon fiber bikes. I design “custom” bikes so I don’t have to follow trends and can make bikes that I believe in. The new SRAM drivetrain shifts better, but it does nothing to get more people on bikes.
I am happy to sit this one out and enjoy my $400 SLX groupset and round dropouts:
My biggest takeaway from the release of the new Transmission stuff is that we don’t have to design for UDH
I believe it’ll be possible to have a nice round dropout that can accommodate Transmission derailleurs and all the other drivetrains with a regular hanger specific to the new dropout. We can call it the Universal Dropout, or UDO
Exactly! SRAM did a disservice to small builders and manufacturers when they left us out of the loop. However, it is a better solution than the UDH spec.
If the insert is slid to the rear of the slot, the 3 mm drop may not be necessary. However, most riders like the insert slammed forward, so this may not be acceptable to most riders.
We are working on a number of variations on this, we think we can come up with a viable retrofit solution.
That’s OK, this isn’t meant to be entry level, it’s meant to be enthusiast and race level. Even the $400 SLX groupset will scare beginners away when they can get an entire bike for less than $400. The hope is that a rider gets into the sport with an inexpensive bike and moves up from there. Maybe 1 in 5 to 10k will enjoy it enough to buy custom.
We took a look at the STEP file, this is about as simple as it gets. Is the flat at the bottom meant to be horizontal, or parallel the the hub/BB CL? Is the flange on the inboard area meant to be the rotation stop?
We have a Transmission drivetrain on order, we’ll print this in plastic first and confirm fit. We’ll also post pics of the progress.
The flat on the bottom is to help clock the dropouts to each other and to the hub/BB CL.
The inboard flange allows the stays to be as inboard as possible. 4mm is as far as the spec allows.
There’s no rotation stop, although I guess the back of the flange would act as one if the knurled ring in the derailleur slips a little.
Now that I think about it, it’ll be necessary to create some kind of dummy insert for the drive side dropout while building the frame.
Can’t wait to see what you come up with. I have a transmission group on order too. It’ll definitely help to see the derailleur in person to understand how it all works.
Incredible stuff y’all are capable of doing here and I for one am totally relying on someone to figure out a dropout for Transmission and make it available to me … just sayin.
The Transmission is cool from like a tech perspective and from a pure burley-ness perspective… but agreed with all Daniel Y’s points about drawbacks and the goal of what WE are doing!!
… just sayin.
