Integrated Flat Mount Dropout (Snap ring/UDH)

This is a rough draft of our hypothetical snap ring integrated flat mount dropout. We will also have a UDH version on the right side available. Are people interested in a dropout that looks like this? It’s important to note that this snapshot is the titanium version with hoods to accommodate 3/4" SS and 7/8" CS, hence the flare at the chainstay tabs. Stainless and Steel will have smaller hoods. Because this will be machined from a solid block of material, they will be expensive. The upside is that they will be more accurate than a 3D-printed or cast part. Please comment your thoughts!

From a previous @mark_pmw post: “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."


Flatmount, my favorite topic :sweat_smile:

It would be great to get a discussion going about how to tackle flat-mount designs as a group. T

A few points of discussion:

  • FM140 vs FM160
  • Asymmetry of the chainstays
  • SS to caliper clearance
  • Aesthetics

I think if we can help PMW constrain the design space, we can end up with a better product. Right now the scope is pretty broad.

@Calvin_pmw are there builders requesting a hooded, FM solution? Do you know if it is for gravel, road, or mtb? TIG or brazed?

1 Like

Looks functionally similar to the Lichen OGQ style which I generally like. For me to pick the PMW version, it would have to be competitive on price. I’d love to see hoods for 19mm chainstays personally!

1 Like

@Calvin_pmw i would love this dropout in Ti since right now I use your tab style and add plugs. So even though they’ll be expensive I doubt they’ll be too much more than the plug and tab dropout cost plus the time.

There are no hooded & machined flat mount dropouts in Ti available right now, as far as I’ve found. The Lichen Mfg ones were the last one I’ve used but the hoods barely fit the needed diameter tubes on the hoods.


I feel like you could make this so much cleaner, lighter, cheaper if it wasn’t designed to accommodate a flat to post adapter. You already have beautiful post mount dropouts so I say go all in on flat mount and get rid of the backsweep and height of the Seat Stay portion. I personally prefer the aesthetics/proportions of your OG plate FM dropouts.


That is a good point. I think a lot of parts fall into the one-size-fits-all trap because builders don’t give enough feedback or direction to the designers.

The reverse also happens: builders have to buy parts and trial and error to see if it works with their application.

Setting more constraints could tighten up the design:

  • minimum CS SS angle?
  • compatible with cable-actuated FM calipers?
  • compatible with post-mount adapters?

An example, with the FM160, rotated forward, we can clear a ~51deg SS angle. This is roughly a 50cm road bike seat tube.

It would be nice to see two versions:

  • one dropout with no SS extension for large bikes
  • one dropout with minimal SS extension for small bikes and mechanical FM calipers

IMO, the whole reason for FM calipers is for aesthetics, but it kinda cancels out when the dropout starts to get really clunky to accommodate all permutations of calipers and ss’s.

I would take my advice with a grain of salt though, we will most likely use 3D-printed FM160 nubs moving forward. But if we didn’t, we would use a hooded FM design.

1 Like

I personally prefer to have the seatstay extension since it avoids any potential caliper interference without needing a vertical bend in the lower seatstay for small frames or even medium frames with a sloping top tube. I’ve had a very close call when using the cast Long Shen hooded FM dropout linked above with no seatstay extension (which looks very similar to what Daniel is using with his 3D nub. Two versions would work too but I don’t think the above version looks bad or overbuilt.


I’ve got nothing against a small extension similar to the lichen or Stinner but make it more inline with the axle so the seatstay isn’t so offset. It seems pretty clear that this and the BoBl system have a large offset and higher extension to accommodate a flat to post adapter/caliper.

I really like the dual lobe design Nick drew up on the paragon UDH thread. If both of these dropouts are being designed at the same time I think it would be great to create an ecosystem that share aesthetics. I think a FM version of nicks design with a long CS lobe would be perfect. Customers will want to run coaxial AXS mullets with flat mount brakes. I know I do.

Add a snap ring DS and a standard NDS that all pair nicely with one another and you have most of the modern options covered


Hit up Paul for the Klamper file! I know he’s given it to several builders and Lichen to check clearances on dropout designs.


Our goal is to have two versions. We are not going to dictate which is used on a mountain, gravel, or road bike, that is really up to the builder. The two versions are outlined at the top of the thread.

We agree the scope is broad right now, but we have to accommodate as many possibilities as we can.

Builders are requesting a hooded FM solution in ti and steel. This is independent of the compact UDH project.

Our designs are equally applicable to TIG or brazing.


We intend to be competitive on price. In addition we have more hanger options and we intend to have a UDH option as well. No problem to fit 19mm stays.

1 Like

We plan on doing it in ti, with a version that will accommodate 3/4" SS and 7/8" CS. It will be completely symmetric, except for a shortened CS tab on the right side. SS and CS will be symmetric about centerline. We’re still in the design phase so they won’t be ready immediately, but with plenty of time for the MADE show.


Our goal is not for the dropout to accommodate a flat to post adapter, though it may incidentally work with a post adapter. The SS angle is the driving factor for this. The OG plate FM dropouts will still be available. This new dropout is in addition to our lineup, as opposed to a replacement.

1 Like

I think we are somewhat confined to the one-size-fits-all trap due to our large and varied customer base. To minimize this we intend to have two versions, as mentioned earlier. Trial and error can be reduced by referring to the step files on our website.

If we are setting constraints, the minimum CS and SS angles must be relatively small to accommodate smaller riders.

As long as a cable actuated FM caliper is designed to FM standards, it will fit any FM dropout. As far as PM adapters, they may incidentally fit, but this dropout is designed specifically for FM. SS angle is the driving factor for whether a PM adapter will fit.

1 Like

Yes, we will have a SS extension intended for almost all sizes of bikes.


It will be completely symmetric, except for a shortened CS tab on the right side. SS and CS will be symmetric about centerline.

Although it would be nice to share aesthetics, these dropouts are so different that it may be difficult to do.

If customers want to mulletize their bike, we will have the options!

1 Like

Here is an updated drawing. It has complete symmetry for both CS and SS and is fully UDH compliant. There are some cons to this design that warrant discussion.

The left side is absurdly thick, requiring a lot of material and machining, making this part expensive. Cosmetically, it looks asymmetric even though it is not.

Would any builders actually be interested in a dropout like this? There are other options for how we could make it. It could be manufactured with a bolt on brake insert which would bring down the cost and make it more machinable.

We could also make the dropout look symmetrical, when it actually won’t be.



The seat stay extensions seem really tall. Maybe they could be as high as the UDH fin.

I might be in the minority but I’d prefer the flat mount bosses be set for 160 rotors and ditch most of the height from the seat stay extensions. At FM 160 I have no trouble with caliper clearance using 9/8” snap ring drops and the flat mount bosses for gravel bikes.


I don’t think symmetry of the dropout is so much the concern as symmetry of the stays relative to the wheel/tire and appearance when looking at the bike from the rear. Nobody will know the dropouts are different when looking at the bike from one side.

@manzanitacycles what is the shortest seat tube you have built with flatmount dropouts? We built a gravel bike with a 400mm seat tube and 415 chainstays on a 1.5 round dropout with FM160. It took very careful planning and a small deviation from the defined FM standard to guarantee clearance for sram and shimano calipers. This was built with minimal seat tube extension above the top tube.

For a part that is intended to be universal I think the seat stay extension is a necessity.



The shortest ST C-C was 360mm for a hardtail. But I bent the stays to get over the caliper.

As a universal part, you’re right that the stay extensions are necessary. But maybe they don’t have to be so dang long :stuck_out_tongue:

It’s just that if the dropouts are going to be really porky as @Calvin_pmw said, then I’d rather stick with snap rings and the FM bosses. But I can see it solving problems for other builders who want to build with hooded dropouts and don’t want to mess with chomping into the their chainstays.