I am trying to implement the PMW UDH into a gravel bike build but I am having trouble aligning the chainstays to hit the rounded portion of the NDS hood. It seems that because the CS plane is offset higher, it tends to miss the hood. I’ve tried finding Chainstays that taper to a smaller diameter to minimize this effect, but I am wondering how others get around this. Could I just lower the NDS Chainstay?
Some details below:
*430mm CS length
*77mm BB drop
*3.5mm positive offset for the actual chainstay plane to the rear wheel axis
*13 mm distance from the bottom of the dropout to the BB center.
*Zona 29er S Bend CS
Also, what is the purpose of the 3.5mm offset? I have the SRAM UDH clearance mask in the model and it does not seem to be close to that at all.
Thanks for the help!
(Will try to attach more photos, but have a 1 photo limit as a first time user!)
First of all, great CAD! The way you called out and position the dropouts and CS locations are very technically precise.
Many builders have had trouble with this pair of dropouts for the reason you posted. It is good that you figured this out in CAD rather than in real life.
You have a steel tapered chainstay, which is less of an issue. Titanium is the most common application for those UDH paragon dropouts, which requires a non-tapered 22.2mm chainstay. That gets much closer to the clearance mask.
The NDS hood is not quite on the right spot. There are three ways around this:
drop both your chainstays another 2-3mm so the NDS hits the hood
you are able to do this because you are using tapered chainstays
clock the NDS dropout up
I don’t recommend this, because your SS hood locations will be slightly off
I really appreciate the detailed response and explanation for why the offset exists! So helpful to talk to someone rather than be in my own head…
It seems like it would be clearer if instructions were just to offset the chainstay if it is needed to clear the SRAM mask!
*Q: Since it’s a steel bike, would you recommend a different style of dropout? It seems like the tricky part will now be to miter the CS different for the DS and NDS. This is my first bike, so I thought going with a integrated brake mount may be easier than going with the other options that seem less straightforward.
(Heh, the terminology is clean because I spent a lot of time studying your CS layout youtube video! Thank you for posting such helpful resources!)
Some updated photos of the chainstays and seat stays fitting!!
Building an asymetric rear is not too much more difficult. I think this will depend on your tooling. Our workflow is:
Bend CS (in your case you are using pre-bent)
Miter CS-Dropout end with tube block
Weld CS to Dropout in chainstay fixture
Dimple Chainstay
Miter CS-BB in chainstay fixture
Mitering the CS-BB at the last step resets the tolerance stack of all the steps before it. That means mitering the stays separately is not much more difficult.
The Paragon sliding dropout is the only other one I would recommend:
Sliders definitely make building easier, and you can easily correct for a skewed wheel. It will also work better with pre-bend stays based on the hood locations. Most pre-bent stays run into crank arm clearance. This is why you see many custom builders bending their own chainstays.
*Does dimpling the chainstays affect the dimensionality of the CS (I think your comment on reducing tolerancing stackup by mitering the CS to BB last resolves most of this concern)?
*Any tips for sizing the chainstay dimple? I am thinking of 3D printing tooling that is shaped to the profile of the chainstay to minimize geometry distortion during the process.
Sliding Dropout questions
Thanks for the tip on sliding dropouts, I like the adjustability!
*Do sliding dropouts work with through-axles and a UDH standard (Looks like there is another part that bolts onto them that interfaces with the wheel?
*I am now realizing the integrated dropouts I currently have in the design don’t have rear rack mounts, which could be a nice feature to run panniers…any recommendations here?
It always affects the tube; that’s why you should do the CS to BB miter last. How much it changes depends on your dimpling setup.
^^^ That setup adds ~4-5deg to the bend unless you have a fixed support block, which only works on straight stays.
I usually expect to get 6mm of additional clearance with a dimple. If you push it too far, the tube will buckle.
There are two distinct topics: UDH compatibility and Transmission compatibility. If you are not planning on running Transmission, don’t worry about it. I wouldn’t even bother with the UDH compatibility.
The Paragon slider is Transmission compatible with this insert:
But only use that if you are planning on using Transmission. It is not intended to be an adjustable slider and impacts the geometry of your bike (lowers the rear axle).
I want to emphasize again: if you don’t plan on using Transmission, I wouldn’t bother with UDH. Dropouts are more expensive, it’s heavier, it makes the frame more difficult to build, and it’s ugly on a steel bike. All my opinion!
