[Request] Hooded UDH dropouts

Hi Mark!

Thanks for joining in the conversation.

You may already be working on this, but I believe I’m not the only builder who would like Paragon to make a hooded UDH dropout with at least the lower flange wide enough for 19mm chainstays.

We’ve been discussing UDH solutions here.

Your current UDH dropout pairs with a flat mount dropout. It’d be nice to have the option to use IS or post mount brakes with the UDH dropout since that’s still the standard on mountain bikes.


I use the syntace 2092 with a 22.2 chainstay. I’m in the minority maybe, but I’d like to see a hooded UDH dropout that’s a bit wider than an inch where it meets the chainstay.

We had a hooded UDH at the 2019 PBE, we may have been ahead of our time. It bombed pretty hard, because few builders knew that it was the gateway dropout for SRAM’s coaxial derailleur. I may have a couple steel ones left if you want to try it. It is 1-3/4" diameter on the right side, 1-1/2" diameter on the left. The two sides are concentric, so the idea is to miter one side of the stays, switch hole saws and miter the other side. Some builders may have seen this as too much work. This dropout meets all of SRAM’s specs for UDH. Photo below. Combined with our BK2016, it will do what you’re asking for.

We are working on a hooded flat mount dropout with integrated brake mounts. It has two right sides that are interchangeable, for UDH and our snap ring hanger. We’re still working on the cosmetics, that’s turned out to be a real hurdle. There’s a lot going on here.

We’re considering two versions, and would like some comments. I’ll call the first the small version. It will be 140 FM, with small hoods for 16 mm stays. It will have clearance for a 160 FM adapter. The large version will be 160 FM, with hoods for 3/4" seatstays and 7/8" chainstays. It will have clearance for a 180 FM adapter. This is the one to put a post mount adapter on.

Fair warning: These will be expensive.


FYI, Fairing makes several tapered 22.2mm w/ different butts. Unfortunately, I think 22.2 stays is a minority, but those tubes might help you get there.

Wow, totally flew under my radar! I like the idea of different sizes left and right. Agreed that the aesthetics are the hardest part of this design. Do you have a CAD drawing or STEP file for review? I can drop it into one of our 3D bike models to help people visualize.


I don’t think that say: 27mm instead of 25 is something unreasonable to request. I can work with 25mm and 7/8 stays. I’m sure it’s also fine for welding, but it’s a bit tight for brazing. There is no good way to make triple bend stays with tapered tubes.

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This is the link to the left side, same as our current DR2065:

This is the .STP file for the right side:
DR2072.STEP (112.5 KB)

A dummy axle for this may be a challenge, as the dropout slots are at slightly different angles. You’ll see when to get the files in your CAD program. I’ll try one of our UDH dummy axles and see how it works.


The hoods on the dropout pictured and our proposed large FM160 dropout both have chainstay hoods 1.04", a bit wider than an inch (26.4 mm), plenty of room to land 19 mm stays.

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My vote is for FM160 since I’ve never had a customer spec a 140mm rotor on a bike, but I don’t build many road bikes.

I like the idea of one brake mount that can use different adapters for flat and post mount brakes.

Has anyone used a flat mount to post mount rear brake adapter? It looks like clearance with the seat stays can be an issue.


See my reply to Nick @manzanitacycles I got mixed up with who was asking for the files.


Post mount on the chainstay is always going to be a clearance issue, and an adapter will probably make it worse. A simple solution is to bend the seatstay to make clearance, but that is another step, and not everyone likes the esthetics of it. Plan ahead!

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Here is the UDH dropout on a bike. Honestly, on an enduro-ey hardtail, the size of the dropout looks OK.

The different-size DS and DNS dropouts also look fine. The challenge is the asymmetric SS and CS. As-is there is no way to hit both the DS and NDS with symmetric stays.

Here is a mockup with asymmetric stays:

For me, the asymmetric stays are a pretty big deal breaker. I can already hear the “my frame is not aligned” emails :rofl:. I would prefer a symmetric style, with a hood similar to the sliding dropout.

What do others think?

  • Are you OK with different-size dropouts?
  • Are you OK with asymmetric SS and CS?
  • Would you prefer symmetric dropouts

For those die-hard UDH supporters it’s your opportunity to speak up and be heard!


Thanks for the hard work @Daniel_Y!

Even though I originally thought an asymmetrical design wouldn’t be an issue, it looks like it could indeed be a problem with customers thinking the frame is misaligned. Plus, there’s the extra work to make it work.

I look forward to seeing what Mark is currently cooking up.

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All these issues with hood style is why I went back to plate style. Arguably stronger too.


There’s some precedent for asymmetric stays, and by effectively shifting everything to the non-drive side a bit you could be doing the work of undoing the net amount of ai-offset in the world.

I kid.

I’ve been thinking about this a lot in a road/gravel context. I drew up some dropouts that were asymmetric (adding some space to the NDS) so that the stays themselves would be symmetric. The dropouts aren’t exactly the prettiest thing I’ve ever drawn, but they look fine when built into a bicycle with a caliper, wheel, and rotor in there.

That being said I don’t think that’s the avenue I would purse for smaller bikes, though I think it’s fine for mountain bikes. Personally I have no objection to asymmetric stays, since ultimately I’m designing bikes and not frames as standalone objects. That’s the direction I’m going for UDH gravel bikes.

I’d love to see a readily-available hooded dropout. Even if it relies on a small amount of fussing with stays, I think it would provide an option for people to experiment with. And the more people who are experimenting, the more options we’ll see out there for solving this problem.


OK, there’s a lot going on here. I thought I had some of these UDH dropouts laying around, but I can’t find them. The clean up purge must have found them. That means if we’re going to do another batch, some changes can be made.

@Daniel_Y and others mention that asymmetry may be a deal killer. I’m not the builder, but I’ll argue that if things need to be asymmetric to build the bike a rider wants, asymmetry is not an insurmountable hurdle.
@manzanitacycles mentioned it may look like the frame is not properly aligned. Good point, but a typical rider won’t see it. It’s just us frame building nerds who will notice.
@DEVLINCC mentioned that asymmetry is why he prefers plate style dropouts, but with UDH and a plate style dropout, asymmetry is still a design element to solve.
@jeremy mentioned he can handle the asymmetry if needed, but offered a solution with wider flanges to get to a symmetric rear triangle.

This last comment gets to the point of PMW making a fresh batch of updated UDH dropouts. Do builders want symmetry enough to buy a dropout that is wider, which is more weight and less heel clearance, or does a narrower, lighter DO justify asymmetry? Full symmetry means making the left side 1-3/4" diameter as well, adding to the weight. It may be possible to use less than 1-3/4" diameter, but as I recall from our original design, we couldn’t meet all the UDH spec with anything smaller.

There are still some things to consider with UDH and round hooded dropouts. To meet all the UDH specs, the right chainstay must meet the dropout fairly high, almost on center. See @Daniel_Y first pic, side view. With 1-3/4" diameter there’s plenty of room to make the miter, but some may not like the esthetics of this. The other thing to consider is that the UDH spec forces rack/fender eyelets higher than usual on the seatstay. Is anyone planning to build touring/commuting/city bikes with UDH? Is this even an issue?

I see this as a project to design an updated UDH hooded dropout. What do all of you, as builders, want? Are there any riders looking at this that want to comment? We can do these in steel for around US$50.00, but it’s not worth it unless we have a clear design consensus and sales to justify the work required.

Please comment!


These are my thoughts:

  • We should narrow the scope of this dropout to mountain bikes
    • bigger dropouts and wider flanges look OK
    • typically shallower SS angle (<50deg)
  • Gravel UDH is just speculation, and the gravel market is way more sensitive to aesthetics. A 1.75in dropout is a no-go in most designs.
  • (opinion) Gravel UDH would only look good 3D printed or with a plate style.

IMO, the only design that would work well is either symmetric (but large) 1.75in style dropouts, or a hybrid hood/plate, much like your sliders design:

Here is as very rough draft:

I think the hoods need to extend in front of the fin, to allow you to attach your SS’s at a reasonable offset

The NDS would need a 1in shoulder to work with brake tabs (the brake tabs might need to be re-desigend as well)


I agree with @Daniel_Y that the scope for now is mountain bikes. A little extra weight isn’t a deal killer for the flexibility of wider flanges to accommodate larger diameter chainstays. Builders who use tapered chainstays can always grind the flanges narrower if they like.

Something like Daniel’s design looks really nice. A hybrid hood and plate looks great.

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This is a great suggestion, similar to @manzanitacycles :

As soon as we depart from a purely round exterior shape, the price rises rapidly. The exterior profile must be machined, as opposed to buying round bar that’s already a usable size and shape.

More questions: Are builders willing to pay significantly more for a dropout shape that’s not round? What are the advantages to a builder with a non-round shape?

I think gravel/road UDH will eventually get here from SRAM, it’s too big a market for them to ignore. The current UDH will work with any derailleur, but perhaps not optimally. People forget that Syntace was originally a mountain bike standard. There’s never been a gravel/road hanger built for it, and nobody notices. Same with UDH.


I think it’s worth the extra expense to make the dropout as compact and light as possible, except keep the wide flanges :grin:

The Syntace system isn’t particularly light either. I bet it’s possible to design something that weighs less. My crummy design got the DS dropout to ~46g.

@mark_pmw How much do you think something like mine or Daniel’s design would sell for?


Price for a non-round version will be roughly $70 for steel. I like your version a little better, because there’s more angular range to land the seatstays. Which brings up an idea, is there any advantage to making the chainstay hood flat, so that the chainstay miter is a straight cut?

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