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As you can see in the pictures my carbon bike has a crack in the frame, between the seatpost and the corresponding screw. I'm told by my bike shop and by an engineer of the bike manufacturer that I can continue to ride it without any concern because:

  1. The crack has nowhere to expand to
  2. There's no load in this part of the bike

I understand 1. and have no idea on 2., but it still makes me nervous the frame may collapse with pretty bad consequences. What do you guys and girls think?

Thanks

enter image description here enter image description here

Crack closeup Crack from afar

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    Hi, welcome to bicycles. Your first photo is blurry because it appears that the focus is set a bit past the top tube; can you re-take that photo in better focus?
    – DavidW
    May 15, 2023 at 13:31
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    I suggest to set your phone for some small fixed focus and move your phone such that the image is sharp. I find it somewhat easier when the autofocus has problems with small objects. May 15, 2023 at 14:13
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    Thanks. I have replaced the first picture with one that shows the crack much better
    – Daniel
    May 15, 2023 at 15:04
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    Can you remove the seat post and get a pic of the area then? When you loosen the clamp, does the size (especially the width) of the crack change at all?
    – MaplePanda
    May 17, 2023 at 5:17
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    There's no load in this part of the bike Then why did it crack? May 18, 2023 at 14:56

2 Answers 2

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Bruh originates from the pronunciation of bro in African American English. In modern internet discourse, it has morphed into a multipurpose interjection that can convey, among other things, disbelief or dismay. Both these reactions are appropriate.

To clarify, I can't see the pictures super clearly, because it can be hard to take clear close up photos. I think I see a crack between the seatpost binder bolt and the wall where the seatpost goes into the frame. "The crack has nowhere to expand to" is an extremely poor excuse. You are torquing the seatpost binder bolt, and I assume it's pressing on the now-cracked carbon. The force exerted on the clamping mechanism may be less because of the crack. At the very minimum, this is a major cosmetic issue that will significantly affect resale value, and this is a premium brand (the logo indicates that this is a Wilier Triestina). I would not accept the manufacturer's answer.

It's possible you were told this by a customer service representative who was misinformed about their warranty requirements. I would continue to seek satisfaction. You could ask a manager at your bike store for advice. You could find a different Wilier dealer if one is convenient. Possibly you could contact Wilier directly and indicate that you are having problems with your dealer, but they may prefer you to go through their dealers.

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    How do these seatpost clamps work anyway? Is the cracked thing even part of the frame or is it a wedge which gets pulled into the frame by the bolt and presses against the seatpost?
    – Michael
    May 15, 2023 at 14:59
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    It might be structurally "safe" because it is unlikely that the top tube will longitudinally split in halves. My biggest concern would be that the clamp arrangement isn't stable and the seatpost might slip. The clamp acts against the seattube which should still be structurally sound, so it might still work if the screw stay in place. What about warranty claims? (Even though I suspect it'll be blamed on overtightening the screw).
    – DoNuT
    May 16, 2023 at 8:46
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    @Michael The crack is on part of the frame. There's a wedge on the inside of the seat tube that presses up against the seatpost. The bolt that's visible tightens against (or into) the wedge, and hence the wedge presses against the seat post and keeps it in place.
    – MaplePanda
    May 17, 2023 at 5:15
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    @Daniel there's no load in this part of the frame I call BS on that. If there's no load, why'd it crack? May 18, 2023 at 14:07
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    @Daniel If you have carbon repair at hand, is there a chance to get it diagnosed by a professional ahead of a potential repair, even if at a small fee? You seem to be honest about it being your mistake (overtightening) and the main aim is to keep the bike alive while riding safely, so try getting an opinion from sb. who does this for a living, most of the answers (including mine) are just educated guesswork. In worst case, you'll pay for a repair but you can keep the bike, which is probably worth more than 500-700$ - or you'll just be fine and know it.
    – DoNuT
    May 22, 2023 at 5:54
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There's no load in this part of the bike

Yeah, not so fast.

Any side-to-side load on the seat post is going to pull that crack wider, and the existence of that crack means those forces will flex the frame in that area in ways it's probably not designed to handle. That flexing will then put stress on the rest of the frame, likely concentrated on the inside of the bolt hole opposite the crack, again a location probably not designed to be stressed like that.

In fact, those very side forces are likely what caused the crack in the first place.

So we get back to

The crack has nowhere to expand to

So the front half of the bolt hole was designed to resist any stress that tries to pull it apart?

Just like the area in front of the seat post itself was designed to resist being pulled apart from side-to-side forces and not crack?

That didn't work so well, now did it? So why would the front of the bolt hole be expected to resist cracking, in an area less likely to be designed to handle that stress? The area between the bolt hole and the seatpost itself should have been designed to resist side-to-side forces and not crack - yet that failed.

How fast did you get your response? This might be a canned response to a design issue the manufacturer doesn't have the resources to correct. A fast reply implies the analysis and consultations necessary to respond were already done. I'd expect an actual analysis and reply to take at least a week, probably even more as I'd think it would have to be pretty well vetted on top of any engineering analysis.

I might be tempted to get a stainless steel hose clamp and some rubber padding and clamp the rear end of the top tube to limit any side-to-side flexing that could cause a new crack to form at the front of the bolt hole.

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