UDH - Standard or Scam?

mark_pmw · June 22, 2023, 10:21pm

This may be a bit of a contradiction: If you want to run Transmission down the road, that means you’re running something else in the meantime. Doesn’t that mean UDH? We do have to care about UDH if we want riders to have options.

Our take on it is that anything we release has to be 100% compatible with SRAM’s specs. That way, when SRAM releases something else down the road, we can be sure it will work.

A lot of individual builders are making their own dropouts, that work for their style or method of building. Some are within SRAM’s specs, others may not be. It’s not enough to assemble the components and say it’s SRAM compatible. There are very specific clearances required; the best way to check these clearances is with CAD software. The latest specifications can be found at https://www.universalderailleurhanger.com/, scroll down to Downloads, there is a drawing and CAD package. Current revision is H.

Our challenge now is making a fully compatible dropout in titanium that will accept 7/8" chainstays and 3/4" seatstays, is relatively light at a reasonable cost, and completely symmetric. We have a design finished, and we have confirmed with 3D prints. We will start machining next week, so builders will have them for bikes going to the MADE show.

Checking weights in our CAD software, the design is less than DR0065, our popular 12 mm round dropout.

Once titanium is done, we’ll do a similar design in steel. This will be easier, because steel stays are smaller that titanium.

Please watch CFF, our Instagram and our website for updates and availability.

manzanitacycles · June 22, 2023, 10:30pm

Not too hard to make. A 3/4" chainstay will need to be offset by about 9mm. You could reduce that by slightly ovalizing the stay as it meets the DO. The flanges in my drawing are 25mm wide, 10mm of that is inboard the inner face of the DO. That shouldn’t interfere with the chain or cassette.

It’d be easy enough to grind down the fin on a UDH hanger to provide to customers who want to run non-Transmission derailleurs.

PineCycles · June 22, 2023, 10:48pm

Totally understand your perspective. The only way you can truly make sure it’ll be backward compatible is by following the specs provided. Maybe the GX variant will be chunkier and utilize all the UDH real estate. Only way to be sure is to stick with the spec.

Not to mention this is what Shimano and TRP are working off and if they come to market with direct mount options, they may also use all the real estate the UDH Spec provides.

I still think there is a place for a TDH but understand why it may not make sense for PMW

PineCycles · June 22, 2023, 11:04pm

Yeah that looks great! My question is, could you extend the hood flange lower if there was less material on the forward stop? Or would it interfere with the derailleur?

If you’re already taking material off the fin, might as well take some off the forward stop too.

no cad on this computer

mark_pmw · June 22, 2023, 11:30pm

I completely agree with you that this is a simple solution that requires minimum modification to the UDH. Many of us are comfortable modifiying components as needed. However, one of the key selling points of UDH is it’s easy availability. If you wreck your hanger on a road trip, do you cut a new one down with your pocket knife? Or keep a pre-modified hanger it your kit? As builders, it’s important to offer riders all the options available, not limit choices. Challenges in building only last as long as the build, challenges in repair and maintenance can last the life of the bike.

manzanitacycles · June 23, 2023, 12:06am

If the flange interferes with the lower part of the UDH then it will interfere with the Transmission derailleur too. The mounting arm on the derailleur gets wide quickly.

@mark_pmw makes a great point. I think a dropout that works for both without any mods is the way to go. A more oval shape or a double lobed shape is probably the best commercial solution.

It’s still fun to experiment though.

Mark · June 23, 2023, 5:04am

Yes please!

Sideways_Viola · June 23, 2023, 9:01am

I have been trying to find the time to design some UDH Dropouts for my frames. I have been following this thread and I feel for all the metal builders as the UDH is much easier to use for composites. Which is great for me, but I feel bad to brag!

Here’s where I’m at so far. The model is relatively parametric so I can hopefully use this as a base for lots of frames.

sikocycles · June 23, 2023, 12:14pm

Daniel_Y · June 23, 2023, 4:54pm

Screenshot 2023-06-23 0945141085×717 124 KB

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.

Sideways_Viola · June 23, 2023, 5:46pm

It’s certainly more challenging for the steel and titanium builders. But the width of it and assymetricality is still a problem for me. Most of my time was spent trying to get a symmetric set up which didn’t require a 17.50mm thick plate of carbon!

manzanitacycles · June 23, 2023, 5:51pm

I agree with @Daniel_Y that the one hanger to rule them all selling point isn’t important. On long off-road rides or bikepacking trips I always carry a spare hanger. And on mountain bike trips I keep a spare hanger in my tool kit. That way I don’t have to rely on a bike shop to get me out of a jam.

Creating a dropout design for a finless UDH seems to be a good compromise. I can provide customers with a spare finless hanger or they can grab a spare themselves and lop off the fin. Either way it’s a good idea to have a spare hanger at the ready.

I’m leaning toward a design that uses a finless UDH on the driveside and a FM160 mount on the non-driveside. Gravel and road bikes can directly mount a flat mount caliper for a 160mm rotor. Bikepacking and hardtail bikes can use a flat mount to post mount adapter for 160mm or 180mm rotors. One dropout to rule them all!

PineCycles · June 23, 2023, 8:25pm

@Daniel_Y sounds like we are on the same page!

PineCycles · June 23, 2023, 8:37pm

Have you considered rotating the brake mount similar to Sour Bikes?

Daniel_Y · June 23, 2023, 9:27pm

This particular dropout (Ogle) was just giving too many problems with flat mounts that I didn’t bother! It would probably work with that tapered CS. This was a titanium bike, so there were not many tapered stay options. With a 22.2 stay, I don’t think angling would help…

GardenVariety · June 23, 2023, 9:30pm

Obligatory xkcd:

Looking forward to seeing the paragon dropout!

project12 · June 24, 2023, 8:04am

It is indeed a challenge to design steel dropouts for UDH. I have built a Vegur for one of the German engineers that worked on the Transmission a couple of years ago and at the time with my soldered plate dropout I couldn’t find a decent way to get the UDH integrated. After having made some 3d printed dropouts he came back to ask if I can give his bike a new backend that is Transmission specific. Just got the parts back from the printer and there indeed a lot more bulky then my previous Paragon circlip capable dropouts. For now they are fine, but I will definitely rethink the design for the next batch.

For the upcoming UNpaved Victor I am more satisfied with the UDH dropout, but these will get a postmount adapter that nicely makes it all symetrical again, somewhat inspired by PVD/44/Scott. I still think this might be the best way to make the flatmount dropouts but I couldn’t get the design right this time before my self imposed deadline ended…

Concerning Transmission: While I still need to ride it I do feel the derailleur is both waaay to big and not very nice to look at, especially on a steel bike, but on Eurobike it even looks massive on carbon non Ebikes. By the looks of it the GX might be a bit more subtle but for the upcoming Victor I am going with a Classified hub and the Rival XPLR derailleur to get both more range and a much smaller profile. [rantmode off]

WHilgenberg · July 7, 2023, 6:47am

Just as a heads-up, we received enough questions asking whether or not we would be making more of our UDH dropout design available for sale that we figured we should make a test batch to see what people think. We just finished them up Wednesday and are now live up on our webstore.

Since we don’t want to just throw something up on the forum without giving back to the framebuilder community, we’ve also published some slightly more detailed thoughts on the UDH standard. As well as full details on the features of the Fastback Dropout.

We’ve also provided files to @BikeCAD so you can see how it all looks put together in a frame.

If there are any more questions that you might have on why we designed the dropouts the way we did, feel free to message me directly or post them up here and we’ll be happy to explain why we did it the way we did it.

mark_pmw · July 7, 2023, 1:57pm

Nicely done! The documentation is excellent, something that will make life easier for builders. I also like your comments on UDH/Transmission. It’s here to stay, so the better we can all adapt, the better for our ultimate customer, the rider.

terraformbicycles · July 7, 2023, 4:13pm

Will these be available in Bikecad soon? I think I might build myself a couple MTB’s this winter for testing next summer, but prefer to use dropouts available in Bikecad.

Are you using chainstay tubing that isn’t 3/4" / 19mm? I generally use this diameter as the 3d yokes I’ve been using are designed for that, but I like to have 2-3mm of excess width so my braze doesn’t pour over onto the side of the dropout. I see in the .pdf that the dropouts are 19mm wide.

Will you also be selling the dummy axle adapter?