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A broken drop outs in HALF (Help I need answers)

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A broken drop outs in HALF (Help I need answers)

Old 06-01-21, 03:53 AM
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SuperPershing
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A broken drop outs in HALF (Help I need answers)

So hello! I have a 2014 Cinelli Mash Parallax. I bought it in 2018 and it gave up last sunday. The rear broke in 2 when I was fixing it. And on the day it felt "heavy" when pedalling. And please guys, help me find answers ( so that I can avoid this from ever happening again.



Now I have 5 Theories on why it broke.

Bike Trainer: I had a bike trainer before the 2020 pandemic started and when the lockdown was imposed, I have biked this everyday for 4 months on a turbo trainer like a minoura 60b? And I saw a article recently that a turbo trainer can potentially break your bike because it doesn't dance from left to right like a normal bike would. Because it is fixed to the trainer so it has a lot of stress in the rear.

Imbalance of the Seatstay: The Seatstay of this bike is not perfect, both are slightly to he left but the chainstay is perfect. So when the wheel is aligned in the chaintay, the wheel in the seatstay are more closer to the right seatstay. So I guess imbance of stress? more stress was in the right side resulting in a failure of years woth of cycling?

Middle Bolt: I just really thought that the middle bolt of the drop outs just caused the initial crack really.

Over Tension: Self Explanatory. Over tighten the nuts

Previous Owners: again I bought this 2nd hand and they said that this frame endured countless of crash (reasons of dents and imbances?)

So yeah, That's my 5 theories and I wish you could help me figure this out and on how can I avoid this in the future. Because this week, I am going to buy a another Cinelli. Thank you!
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Old 06-01-21, 07:08 AM
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Add possible overheating at the factory... That's where many dropouts have broken before. Campy Strada 1010s and 1010Bs are known for this. The hole right at the point of minimum cross section isn't a help either. The cheap fix is to add a gusset spanning the two stays and avoids the chain. The better fix is to replace the drop out. Andy
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Old 06-01-21, 07:27 AM
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Perhaps I'm being dense, but I don't understand what you're going to do with that frame, and therefore, what your concern is to prevent a recurrence. Are you going to have the dropout replaced? Or get a new frame or frame, and don't want it to break?

FWIW, I'd look carefully at the costs before replacing the dropout. You could probably buy a new (used) bike for the cost of stripping the frame, getting a new dropout welded in, and repainting the frame.

I can't see how overtightening the wheel skewer/nut could break the dropout (unless the frame was mis-aligned, and even then, that's on the frame build and not the skewer). You're basically clamping down on solid metal -- it's not going to squeeze out.

Trainer or previous abuse seem the most likely. Buy a cheaper bike with a stouter frame for the first failure mode, and don't buy a beat up bike for the second.

Also FWIW, when one of my dropouts broke, the mechanic responsible for replacing the frame blamed poor heat treatment, in accordance with Andrew's suggestion.
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Old 06-01-21, 04:34 PM
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This is a proper track dropout.


Note the amount of material surrounding the slot for the hub. Also note that the section the hub clamps onto is not machined thinner as if to accommodate a shim or axle-guide. Also note that it doesn't have any holes drilled into the load-bearing portion.

I can't say what broke your dropout, but from its appearance its failure doesn't surprise me. Maybe you can get Cinelli USA to warranty it.
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Old 06-01-21, 08:56 PM
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Originally Posted by oldbobcat
This is a proper track dropout.


Note the amount of material surrounding the slot for the hub. Also note that the section the hub clamps onto is not machined thinner as if to accommodate a shim or axle-guide. Also note that it doesn't have any holes drilled into the load-bearing portion.

I can't say what broke your dropout, but from its appearance its failure doesn't surprise me. Maybe you can get Cinelli USA to warranty it.
+1 That track end (it's not a dropout) looks designed to break. Crash the bike a few times, spend time on a trainer and it's cooked and done. That (perhaps threaded) hole just in front of the slot? Let's remove material and provide a stress riser at the key location. If you buy another Cinelli with the same track ends, treat it carefully, crash as little as possible and keep it off the trainer.

If that hole was for an axle stop to prevent the wheel being pulled forward by a strong rider - well they got it all backwards. Strong riders need strong track ends and tightly secured hub nuts first and foremost.
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Old 06-02-21, 02:37 PM
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Originally Posted by 79pmooney
If that hole was for an axle stop to prevent the wheel being pulled forward by a strong rider - well they got it all backwards. Strong riders need strong track ends and tightly secured hub nuts first and foremost.
That’s not what the screw is for. The Parallax is an aluminum frame, 7075, I believe. I bought one in 2018 as well (but might be a different model year from the OP’s).

The track end itself could be a different alloy from the tubes, but it’s aluminum. To make it tougher, they put in a stainless steel insert, held by three screws. That’s why the track end is milled or forged a little thinner in the area surrounding the axle slot. Presumably, that insert was removed for pictures after the crack appeared.

FWIW, my bike has had no issues, structural or otherwise. But it’s been treated gently. I rode it quite a bit in 2018, only about five times in ‘19, twice in ‘20, and a little so far this year. It goes out in good weather, on mostly smooth roads. 780 miles on it, give or take a few.

It’s troubling to see a failure like this, and the kind of thing that will not be cheap to repair—because 7075 will need to be TIG welded, whereas a steel dropout could be fixed with MIG or even a gas torch.

Since the frame’s history is not really known, it’s hard to say what’s the most likely cause. Also, I’d never heard of the suspicion that indoor trainers can cause this, but it seems plausible.

Last edited by Broctoon; 06-02-21 at 02:42 PM.
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Old 06-02-21, 03:04 PM
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What were you 'fixing' when you broke it?
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Old 06-02-21, 04:31 PM
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Originally Posted by Broctoon
I’d never heard of the suspicion that indoor trainers can cause this, but it seems plausible.
I got a bit interested in a trainer last year because of the situation but then I dropped the idea. But reading up on it, people are concerned with the trainer mount point in connection with pedaling while standing on the bike or even doing sprints on their trainer.

Point is, the trainer keeps the axle mount stiff and if you pedal while standing on your bike, never mind rocking it like people do when going uphill (really trying to rock because the setup allows little of that), it can't be good for the frame ends at the mount points, namely the rear ones.

Trainers were developed for bike training while sitting in the saddle which some people just don't get. Or you can stand up for a bit but don't get the idea that you can go humpty dumpty on pedals while rocking the bars. IMO if I should make a guess, it would be the trainer that did that crack. Really no reason it should happen otherwise in a normal intended use. I doubt if the frame was in warranty period, it would be replaced if the company knew the bike was used on a trainer.

I think people with expensive frames should get some cheaper and sturdier bike for use on a trainer if they want to race it on it. Doesn't most of the touted features of the high end frames count for nothing when used on a trainer anyway? You can start with the frame being aero or having those rough road dampening features and if you gonna test the frame torsional stiffness, that's when you are liable to damage it.

Last edited by vane171; 06-02-21 at 04:39 PM.
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Old 06-02-21, 05:33 PM
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Originally Posted by pdlamb
Perhaps I'm being dense, but I don't understand what you're going to do with that frame, and therefore, what your concern is to prevent a recurrence. Are you going to have the dropout replaced? Or get a new frame or frame, and don't want it to break?

FWIW, I'd look carefully at the costs before replacing the dropout. You could probably buy a new (used) bike for the cost of stripping the frame, getting a new dropout welded in, and repainting the frame.

I can't see how overtightening the wheel skewer/nut could break the dropout (unless the frame was mis-aligned, and even then, that's on the frame build and not the skewer). You're basically clamping down on solid metal -- it's not going to squeeze out.

Trainer or previous abuse seem the most likely. Buy a cheaper bike with a stouter frame for the first failure mode, and don't buy a beat up bike for the second.

Also FWIW, when one of my dropouts broke, the mechanic responsible for replacing the frame blamed poor heat treatment, in accordance with Andrew's suggestion.
I'm going to buy a new Cinelli. It's too dangerous to be fixed
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Old 06-02-21, 05:35 PM
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Originally Posted by cxwrench
What were you 'fixing' when you broke it?
When I was going hone, done a 92km loop with my Cinelli I noticed that it "feels hard" to pedal even thou my gearing was just 48x17, my climb setup. I usually go 51x15 so I know when it is heavy or not and I was kinda heavy. And when I got home I was going to fix the chain tension thus I discovered the crack.
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Old 06-02-21, 05:39 PM
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Originally Posted by SuperPershing
"feels hard".
from the crack?
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Old 06-02-21, 05:40 PM
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And also, I have discovered 2 new cracks ON THE LEFT Drop outs. not on the failure, right.

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Old 06-02-21, 05:46 PM
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Originally Posted by Troul
from the crack?
Yeah might be. It just feels hard and weird even thou the road was flat as paper
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Old 06-02-21, 08:48 PM
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Originally Posted by SuperPershing
I'm going to buy a new Cinelli. It's too dangerous to be fixed
As you probably know, the MASH collaboration has ended. But the Cinelli Tipo Pista sure is a nice looking frame!

Also, is your fork in good shape? If you’re going to scrap the Parallax and interested in selling its fork, please DM me. (Too soon?)

Last edited by Broctoon; 06-02-21 at 08:52 PM.
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Old 06-02-21, 09:10 PM
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Originally Posted by vane171
I got a bit interested in a trainer last year because of the situation but then I dropped the idea. But reading up on it, people are concerned with the trainer mount point in connection with pedaling while standing on the bike or even doing sprints on their trainer.

Point is, the trainer keeps the axle mount stiff and if you pedal while standing on your bike, never mind rocking it like people do when going uphill (really trying to rock because the setup allows little of that), it can't be good for the frame ends at the mount points, namely the rear ones.

Trainers were developed for bike training while sitting in the saddle which some people just don't get. Or you can stand up for a bit but don't get the idea that you can go humpty dumpty on pedals while rocking the bars. IMO if I should make a guess, it would be the trainer that did that crack. Really no reason it should happen otherwise in a normal intended use. I doubt if the frame was in warranty period, it would be replaced if the company knew the bike was used on a trainer.

I think people with expensive frames should get some cheaper and sturdier bike for use on a trainer if they want to race it on it. Doesn't most of the touted features of the high end frames count for nothing when used on a trainer anyway? You can start with the frame being aero or having those rough road dampening features and if you gonna test the frame torsional stiffness, that's when you are liable to damage it.
There are literally tens of thousands of people who use their regular bikes on trainers yearly, incuding some extremely lightweight carbon road bikes. All without issues. At times I have been on Zwift with over 45,000 other users going all humpty dumpty on their pedals and rocking their bars.
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Old 06-03-21, 05:09 PM
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Yikes that looks scary.
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Old 06-03-21, 06:46 PM
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Wondering if the metal you are showing is the dropout or a steel protective piece like shown here. Your picture looks to be missing the rivets which might indicate a missing piece. Torquing the aluminum directly could stress in unusual ways.
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Old 06-03-21, 08:24 PM
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Originally Posted by stevel610
Your picture looks to be missing the rivets which might indicate a missing piece.
They’re not rivets, but tiny screws. The outer doubler plate has threaded holes, and the inner one is dimpled for countersunk screws, with 2.5 mm hex (Allen) heads.

I hope these were in place for the OP. If not, and he rode without them, I think we know why cracks appeared.


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Old 06-03-21, 09:45 PM
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Originally Posted by stevel610
Wondering if the metal you are showing is the dropout or a steel protective piece like shown here. Your picture looks to be missing the rivets which might indicate a missing piece. Torquing the aluminum directly could stress in unusual ways.
Originally Posted by Broctoon
They’re not rivets, but tiny screws. The outer doubler plate has threaded holes, and the inner one is dimpled for countersunk screws, with 2.5 mm hex (Allen) heads.

I hope these were in place for the OP. If not, and he rode without them, I think we know why cracks appeared.


Of course the plates were there. I just removed them for further inspection. And also the fork is already sold, Sorry (
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Old 06-03-21, 10:19 PM
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Are you going to continue using your trainer?

Do you have any machining capabilities?

In theory, one course of action would be to grind a V-Grove into all the cracks, then weld up.

Decide if you wish to keep the steel plates, or fill flush, then grind back down flat.

Then just use the old frame on the trainer, and get a new one for the road.
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Old 06-03-21, 10:35 PM
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This is just a theory. But stainless steel and aluminum together can cause galvanic corrosion. The Aluminum is the first to weaken but combined with the added stress both cracked. When you are riding outside your sweat has other places to go. But on a trainer in a small hot room things are going to start being like a sauna pretty quick.
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