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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:
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
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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.
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.
