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God damnit, that was an expensive ride.
Now I’m trying to find one identical to this so I can use it for parts. I just hope this isn’t a common issue with this frame and that I just got unlucky with mine.
Would’ve been an easy fix if the frame were steel - but from what I understand, welding isn’t really an option with these alloy frames.
Holy. Ballz. Between you and @DerPlouk@lemm.ee, this is starting to resemble a generalized design flaw. DerPlouk's break looks like more like a stress riser, whereas yours looks like an HAZ. Aaaannd that is the about the outer limit of my metal failure analysis skills.
Are there any welders or metallurgists in the house? I would love to read a failure analysis of how and why this happened right at that spot.
Strain-stress for aluminum had a finite lifetime limit, so after X stress over the life of the part it will break, where steel is almost infinite as long as it's below the per instance maximum
Someone aluminums!
I mentioned this to chatGPT earlier, and it correctly guessed the exact location where the frame cracked, so I assume it’s simply a high-stress zone. Makes sense though - when I’m sitting down and bouncing over heavy rocks and roots, that’s the part of the frame that takes the brunt of the force, preventing the rear triangle from folding in.
I’m not the smallest guy, and I usually have a heavy backpack on, which surely doesn’t help either. That being said - the frame is rated for 120 kg, and I stay well below that, so it's most likely a manufacturing defect.
My (regular) fat bike frame broke at the same place. Are you tall and was this a large size frame? Mine broke when I stood up on the pedals: the whole body weight + the pressure applied and transmitted through the chain, pulling the wheel axis frotnwards. I have the feeling long frames are more likely to break this way, and fat bike frames too as the chain stay has to make a big curve to leave room for the tire, which weakens the tube and its ability to respond to tensions which are not any more directed in the 'right' way.
Aww, sorry to see that. I know you love your bike, I've seen a few posts on it :(
Pardon my ignorance, but why wouldn't welding be an option? It has clearly been welded at factory already.
My understanding is that in the factory, after welding, the entire frame is heat-treated to restore its strength and make the material properties uniform throughout. This is especially important for aluminum alloys, which lose significant strength in the heat-affected zone around the weld.
If you weld it again later, you're exposing that area to high temperatures without reapplying the same post-weld heat treatment which weakens the surrounding material. So while it’s technically possible to weld a cracked aluminum frame, the area around the weld will likely be much weaker unless you can re-heat-treat the whole frame.
This is a load of baloney. If it was welded before, it can be welded again. You only need to heat the effected zone not the whole frame. Also put a sleeve over top and add more weld. Heat treat isn't anything fancy. Get a temp gun and a propane torch. Get it to temp and let it cool slowly or quickly or both. depending on the spec you find.
The only reason they cook the whole frame is because it's easier from a manufacturing point of of view.
Sounds like a job for JB Weld.
I've considered it but I don't think it would last.
Preheat, expansion contraction control , and post heat is needed. But you wouldn't have to heat treat the entire frame, just this area/members of the weld. There are specialized welder dudes that you can probably find, but if its breaking from factory it will need extra gussetting. The pictures I saw the angled arm going up to seat post is more flat than vertical. Rather than bump force going up to the seat neck, it looks like it acts as a fulcrum and the bump would stretch the lower arm instead
This, if the factory can do it then a skilled craftsman can as well. Talk to some local fab shops, I'm sure you can find someone skilled in AL welding that can fix you up
The bikewrench community might have a fix. While I never saw a chainstay break like that before, I have seen breaks in load-critical joints such as downtube to bottom bracket shell and headtube to downtube.
My fix was to make an internal sleeve joint using carbon steel pipe. I would then epoxy it in place with 3M 5200, the same glue used to hold sailboat keels in place. Shipwrights also refer to it as Devil's Glue, because it's some tenacious stuff. The shaping on that tube complicates this fix, but some careful shaping might get you to done. The only reasons I even attempted these fixes were because the bikes had huge sentimental value to the owners.
Another possibility could be a internal shim made of G10, wrapped in ~5 to 8 layers of biaxial fabric (glass) wetted out with 2-part epoxy. Once cured, it would be ridiculously strong in all axes, for tensile, compression, and shear. Source: this is how I repaired a broken mast spreader bar in the middle of the ocean.
Effort-wise, you might be better off getting a new frame and using the original as an organ donor.
Also, YMMV, fix at your own risk, blah blah blah taco.
Edit: a word
It's clearly those zip ties that did it. 😄
Hot glue and gaffa tape 👍
Oh trust me, if there was a DIY solution for this - no matter how ugly - I'd definitely try it. I even considered bolting a flat bar of steel on both sides of it. I just don't think anything like that would last longer than few kilometers.
