Bicycle Mechanics - derailleur clamp mark on carbon fiber seat tube

I just purchased a used 2007 Bianchi 928 SL frame and while building it up, noticed a dent in the seat tube where a derailleur clamp had been. It appears as if the tube is dented and pinched, but I'm not sure if this is just the clear coat or if the tube itself has been structurally compromised. Is this something I should be worried about?

http://johnrpowell.net/images/carbon-seat-tube.jpg

nice books nerd

lal

I think it will be OK to ride.
I don't understand why some manufacturers use clamp-on derailleurs on carbon fiber frames when most use a "braze-on" type. Carbon fiber usually has very high tensile strength but lower compressive strength.

Al

I'm hoping that first comment was a joke. Do people really spend their time trolling on this thing just to make the first pointless statement on every message thread? But I digress...

I definitely agree--it makes little sense to me why manufacturers continue to use clamp-on derailleurs in some instances. The 928 SL was one of their higher-end frames for that year; you'd think they would use the most sensible technologies on it.

Here are a few clearer images of the area in question:

http://johnrpowell.net/images/framedamage3.jpg

http://johnrpowell.net/images/framedamage2.jpg

http://johnrpowell.net/images/framedamage1.jpg

I'd take it to a reputable shop that deals with carbon - and have them test it for any damage below the outer coating. Anyone who is planning on attaching components to a carbon-frame or fork MUST have a suitable torque-wrench(s). Just a little over tightening and you can kiss any warranties bye, bye. As well as possible getting you injured or killed.

Torque-wrench, and learn how to use them.

<EDIT> The trolls are part-time. Relax.

I wouldn't sweat it.

It appears to simply be cosmetic, and in any case isn't in a critical, highly stressed area. What I would do is find some decorative sticky material and make a band to cover it, and possibly a second higher on the seat tube to make it seem part of the original frame decoration.

I'm not a fan of carbon because of it's tendency to fail catastrophically without warning, but I wouldn't worry about this causing a failure in my lifetime.

I'd have it looked/listened at. The OP said it was a discernible bend and scarring. That's grounds for a full check-up. At least in my book.

Let's be real, it might have been cause for concern before buying the frame, but that bridge is already closed. Yes, he could bring it to a mechanic, but very few (if any) LBS mechanics are any more qualified or equipped to pass judgement on this than he is.

he could apply the adage "if in doubt, throw it out" but where does that get him. In assessing the his real risk he can apply a bit of risk assessment logic. Where the consequences of failure would be very serious such as a fork steerer only a tiny risk is acceptable, but where the consequences of failure are low, a greater amount of risk would be acceptable.

In this case, while the chances of failure aren't known, we do know that it isn't a highly stressed area of the frame, and unlikely to fail suddenly without some warning. In any case a seat tube failure is unlikely to cause a crash and injury, so from a risk assessment standpoint riding this frame isn't any more unreasonable than riding any bike out in traffic.

There is no "test" that can be performed for damage by a LBS. From the pictures, this is only clearcoat damage, but it's also an example where someone applied far too much torque to the derailleur clamp.

I'd be inclined to sand the area with 600-1000 grit sandpaper (wet) to smooth up the ridges.

I have three CF frames that use clamp-on FDs and I've never had any problem at all. The problem is ignorant mechanics.

I prefer to use a Campy or Shimano clamp-on adapter with a braze-on FD. I consider the adapter part of the frame and rarely remove it.

There is no "test" that can be performed for damage by a LBS.

What if I told you we had an x-ray machine?

What if I told you we had an x-ray machine?

And?

X-rays are not capable of detecting stress micro fractures in carbon structures.

The OP will not be able to get any qualified, meaningful determination of the structural damage (if any) at anything below what the frame is worth.

It's a calculated risk whether to ride it or not. It's the OPs risk, and therefore his judgment call.

As I said earlier, in his shoes I'd ride it and not sweat it. He could and should cover the damage, both for cosmetics, but more importantly so that water doesn't enter the matrix through the cracked clear coat. Assuming he'll be mounting a FD on the frame he might see if he can get the same model as was used previously, though it won't make much difference either way.

BTW- I'm not being fatalistic, or taking a casual attitude about the possible risks. If I found similar damage in a more critical area, near a head joint, or on a fork, I'd scrap the frame without giving it a second thought.

Thanks for all of your help and comments. I took the bike to a very reputable bike shop in my area that is a Bianchi dealer and one of their head mechanics inspected it. His opinion was that the damage was structural and that the carbon fiber was cracked. He concurred that it's not in a high-stress area, but it is likely that the crack would grow over time. I could hope for the best and ride it, but considering how much money I paid for it, I'm just going to get my money back and return to my reliable aluminum frame for now.

Thanks again!

Sounds like a good plan. It sucks when you don't feel confident with your frame. You should enjoy the speed on a nice downhill and not have to worry if it's your last. :)

And?

X-rays are not capable of detecting stress micro fractures in carbon structures.

The OP will not be able to get any qualified, meaningful determination of the structural damage (if any) at anything below what the frame is worth.

It's a calculated risk whether to ride it or not. It's the OPs risk, and therefore his judgment call.

As I said earlier, in his shoes I'd ride it and not sweat it. He could and should cover the damage, both for cosmetics, but more importantly so that water doesn't enter the matrix through the cracked clear coat. Assuming he'll be mounting a FD on the frame he might see if he can get the same model as was used previously, though it won't make much difference either way.

BTW- I'm not being fatalistic, or taking a casual attitude about the possible risks. If I found similar damage in a more critical area, near a head joint, or on a fork, I'd scrap the frame without giving it a second thought.

So the fact that colnago provides x-rays with their forks to prove that their are sound is just a marketing exercise?

Not sure how much you paid for the frame, but you could send it to Calfee and have them look at it and repair it if needed.

Repair I think would be about $200 + $75 for clearcoat.

http://www.calfeedesign.com/howtosendrepair.htm

Not sure how much you paid for the frame, but you could send it to Calfee and have them look at it and repair it if needed.

Repair I think would be about $200 + $75 for clearcoat.

http://www.calfeedesign.com/howtosendrepair.htm

And we are trust these people and why? I wouldn't accept a "repaired" carbon-frame. I'd junk it, return it, anything but trust it enough to ride it. And I like their legal boilerplate:

"Under no circumstances shall Calfee Design be liable for any damages or injuries incurred by the use of the Repair Servise. This includes, but is not limited to: lost profits, lost savings, and incidental or consequential damages or injuries arising from the use of, or inability to use this product. The limited warranty set forth in this agreement may not be extended or modified by any Calfee Design Dealer, Agent or Employee. Calfee Design does not assume any liability or make any warranty except as stated in this limited warranty. This warranty gives you specific legal rights, and you may also have other rights depending on your state. Some states do not allow limitations on the duration of implied warranties, or the limitation or exclusion of incidental or consequential damages; therefore, the limitations and exclusions set forth in this warranty may not apply to you. "

:eek: :twitchy: :eek:

And we are trust these people and why? I wouldn't accept a "repaired" carbon-frame. I'd junk it, return it, anything but trust it enough to ride it. ...

Uh, I would trust them because:

"We are proud to offer the benefit of our 20 years experience with composites to the owners of all carbon bike frames. Many major carbon frame companies refer riders to us for their frame repairs, and to help solve design issues. Hundreds of bike shops from across the U.S., Canada, Asia, and Europe have been able to provide their customers with an affordable alternative to Crash Replacements.

Our unique molding process uses the best quality 3k carbon fiber weave to create forms that are shapely, lightweight, and extremely strong. From minor scratches to stuck seatposts to frames destroyed by the dreaded endo or that startling encounter with the garage door; we've repaired over 2,100 frames since 2003."

Also, they built my bike and it hasn't fallen apart or had a catastrophic failure.

And we are trust these people and why? I wouldn't accept a "repaired" carbon-frame. I'd junk it, return it, anything but trust it enough to ride it. And I like their legal boilerplate:

"Under no circumstances shall Calfee Design be liable for any damages or injuries incurred by the use of the Repair Servise. This includes, but is not limited to: lost profits, lost savings, and incidental or consequential damages or injuries arising from the use of, or inability to use this product. The limited warranty set forth in this agreement may not be extended or modified by any Calfee Design Dealer, Agent or Employee. Calfee Design does not assume any liability or make any warranty except as stated in this limited warranty. This warranty gives you specific legal rights, and you may also have other rights depending on your state. Some states do not allow limitations on the duration of implied warranties, or the limitation or exclusion of incidental or consequential damages; therefore, the limitations and exclusions set forth in this warranty may not apply to you. "

:eek: :twitchy: :eek:

Such "legal boilerplate" is probably typical for most types of repairs (it's not restricted to repairs of carbon frames).

True, but I'd still feel I was riding on borrowed time. So I'd be rid of it. The OP is off to return his. His option - and what I'd do too. If I had that option available. Otherwise I'd junk it and take my lumps - making sure to better inspect such before money was exchanged.

I have a 928 waiting to be built up and I was concerned about that as well.
http://img20.imageshack.us/img20/5894/photo113z.jpg

hurry up and get it built before the snow flies!