I have very recently started picking up frame design within Fusion 360. I have limited/moderate experience in Fusion outside of frame design. I know a decent bit about geometry but am starting to realize a lot of the intricacies I did not know about frames until coming here.
After browsing the forum for a bit, I have stumbled into the conundrum of rear dropouts and have a couple of questions regarding decisions in that area. I primarily have been wanting to design road and gravel frames with compatibility for SRAM and Shimano 1x and 2x road and gravel groupsets.
The concept of UDH seems great, but I’ve read a little about the practical application on metal frames being tricky. Is it worth it to try and design a dropout that uses UDH?
If UDH is not being used, is there another hanger that is worth using instead?
I’ve noticed some brands (specifically Surly) use a hanger that is built into the frame. For a steel bike is this worth it or is a separate hanger a better decision?
Are there models of dropouts I can add into my fusion models for the time being that are compatible with specific hangers? I don’t want to infringe on anyone’s copyrights, patents, or trademarks but if there is a premade option I can add that would be good to know.
Any resources into this topic as a whole would be greatly appreciated as well. I am trying to learn as much as I can right now so I can make some educated decisions on the topic.
P.S. A big shoutout to everyone here because this is one of the coolest forums I’ve ever seen!
depending on the dropout, you may need to build your bike asymmetrically ( see allotec cast dropout)
If your stays are symmetric, it pushes the non-drive-side chainstay outwards by 3mm, which causes problem with flatmount bosses
The third reason is subjective: it’s large and ugly.
Some builders use paragon’s snapring hanger on their 3D printed dropout designs. For example, No22’s dropout before they moved to UDH
Some Italian builders do this as well. For Surly, it might be tradition or for cost reasons. Personally, I don’t think it’s a good idea.
IMO, Paragon’s 1.5in round dropout is the best starting point for a dropout. Its easy to design for and build around. The dropout has wide hoods and a large area to land your chainstays and seat stays.
Paragon provides their CAD files on most of their products:
Thank you so much for the insight!! I appreciate the direction.
Makes a lot of sense. The flatmount bosses would harm compatibility with disc brakes, correct?
I can see how it for sure strays from design concepts cycling has had in the past. However, part of me wants to believe with the “steel renaissance” that is occurring right now, dropouts like this may be a stylistic highlight of this era. Sorry for getting philosophical!
Thank you, this looks like a good starting point for me to research!
My thinking as to why it’s a bad idea would be because in the case of a crash, there are two outcomes worse than snapping a hanger that can happen.
The rear derailleur takes the force of the impact and needs to be replaced.
The “on-frame” hanger needs to be repaired/replaced or in the worst case the frame needs to be replaced (guessing that is unlikely for steel though).
This is great! I will have a look and throw them into fusion to mess around with.
Sorry to respond to some of the answers with more questions. Thank you for all the help you already provided though, your response got me a lot further than my attempts to explore the caverns of the internet did.
Bolt-on hangers only came about when bikes started to use aluminium and the all-in-one hangers would snap and couldn’t be brazed back on. Steel one-piece handers are generally ok, because they can bend (a moderate amount) without causing any damage. Bolt-on ones are fine too, but since they are usually aluminium they will break instead of bend if you knock it hard (usually the least of your worries if that happens, mind you). Apples and oranges.
UDH is great as a concept, but as Daniel said they’re not optimised for form and function when using skinny steel tubes. It works fine, but makes things look odd and building can be a little more complex.
Don’t worry about copyright and stuff, if it’s for personal use it’s pretty much fair game. If you’re selling frames you may have issues, but only if you out-right copy someone else’s design (using someone’s hanger in your own dropout would be fine unless they’re really litigious).
I have snapped a hanger or two and I can confirm that the hanger was the least of my worries!
I did notice how large the paragon dropouts were, I am interested to see what they will look like on the next render I do for a gravel frame.
I appreciate that, as of right now I am just trying to learn as much as I can so having the ability to use dropouts from others is great modelling practice. If I was to sell frames (hopefully one day, probably not a day soon), I would try to make my own by that point.
I think all the advice here is sound. The only thing I’d add is that if you’re just starting out with building frames then for the first few I’d just use an off-the-shelf dropout. There are so many things to learn in framebuilding that trying to design a dropout from scratch will end up being a massive distraction (ask me how I know).
I’m not saying don’t do it, just that I wouldn’t do it for the first few frames I’m building.
My first few frames used sliding dropouts.
Partly because I’m a singlespeed enthusiast, but also because the brake mounts are part of the sliding insert, so I didn’t have to worry about needing a brake mount fixture.
I can highly recommend PMW’s DS1001 (or one of the other variants) and they have a great selection of inserts.
At this stage, it can be helpful to explore the various commercially available dropouts and BikeCAD makes it easy to swap in and out most options from Paragon, Allotec,Tange and others: Dropouts (Choosing from static drawings) | www.bikecad.ca.
Great suggestion! I totally forgot about this. Installing the brake mounts, especially flatmounts, is probably the hardest thing to design and fabricate. Sliders remove several steps and a brake fixture.
I often use Paragon Polydrops (PD100) for exactly this reason. You can pretty much just design for axle spacing then leave decisions about QR vs thru-axle and ISO/PM/FM 'til later. Also future proofs the frame to a certain extent.
