The Chainlink

Q: Determining the structural integrity of a carbon fiber frame. A: Pirate gold

I recently purchased my first full carbon fiber frame, YAY! But, a day after I bought the bike I was visiting a friend and didn't have a safe place to lock up so I decided to bring it into his apartment instead. As I was bringing it up the stairs I slipped and the metal door to his building slammed into the rear if the bike. One of the chainstays hit the door jam hard enough to leave some paint on the stay. I scrapped it off with my fingernail and it looks fine but I am worried I compromised the carbon.

Since I am new to carbon frames and know how delicate they can be, yes I use a tension wrench, how can I properly inspect the bike to make sure it is ok? I looked at it with a flashlight and everything looks ok, no cracks in the gelcoat paint, no scratches, no fractures that I can see with the naked eye. I went on some blogs that scared the piss out of me, talking about how impossible it is to tell if there is any damage without using an ultraviolet light to see small cracks and separation of the carbon layers on the inside of the frame.

Needless to say I feel like an idiot but I would rather make sure the bike is ok before putting it through its paces again. Any advice would be appreciated.

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RIDE THE DAMN BIKE... carbon fiber is not that fragile

Take it to a local bike shop and get it looked at if you are really that worried about it.

Ride it, keep an eye on it.  

If it starts to crack then make tomato stakes out of it and buy a steel-framed bike. 

Michal is spot on with this one; carbon is not fragile and unless you have a divot in the gel coat or paint that exposes carbon weave or a visible crack you are fine.  Carbon is surprisingly tough and gets a bad rap from those who do not understand it's properties.

If you are real nervous about it you can preform a tap test, the most basic test of a composites structural integrity:


Take a coin, any coin but a Canadian one as they are unreliable at best, and tap the same area on the other chain stay where the damage is and pay attention to the noise it makes.  Now tap the area in which you suspect damage and compare the tone and if it sounds the same and not flat or hollow and there is no obvious physical damage just go with it.

I know that test seems stone age but it one of the accepted methods of checking a composite surface or structure.

Michael A said:

RIDE THE DAMN BIKE... carbon fiber is not that fragile

I figured I was being a bit overly protective and all. I will say that there are more warning labels on this thing than any other bike I have ever owned or worked on. There is a freaking sticker near every bolt with proper torque ratio on it. I actually find that pretty f-ing helpful, but it does make me a bit more cautious when shit happens to it.

Although, if one day the stays snap off and burst into flames while I'm conveniently doing 60mph down Damen bridge, I'm blaming you Michael. 

I will gladly take responsibility for your frame coming apart at 60 mph or above, while we are in this little fantasy world of yours would you like to BUY that bridge?

Jeff Schneider said:

Determining


If your reply was to correct my spelling, you have failed me sir.

Michael A said:

I will gladly take responsibility for your frame coming apart at 60 mph or above, while we are in this little fantasy world of yours would you like to BUY that bridge?

Only if I am legally allowed to throw virgins off it and reap the rewards it might or might not bestow upon me.

It also does not instantly de-bond after a certain amount of UV exposure.

Nor does it 'explode.'

It also has really good wear characteristics, better than aluminum in my opinion.

It is a well known fact that I am not a fan of carbon bikes but for no other reason beyond pure personal preference as a matter of style and cost.  It is strong, light, comfortable, ages well if maintained and is a very durable material; I think that may be why they make so many aircraft parts out of it...

Michael B said:

Carbon fiber is also repairable which is something ignorant people don't seem to realize. 

But do they make sexual aides out of it? I mean, if they use carbon fiber for aeroplanes than why not something that would also get some serious frequent flyer points? I want that 2013 catalog.

notoriousDUG said:

It also does not instantly de-bond after a certain amount of UV exposure.

Nor does it 'explode.'

It also has really good wear characteristics, better than aluminum in my opinion.

It is a well known fact that I am not a fan of carbon bikes but for no other reason beyond pure personal preference as a matter of style and cost.  It is strong, light, comfortable, ages well if maintained and is a very durable material; I think that may be why they make so many aircraft parts out of it...

Michael B said:

Carbon fiber is also repairable which is something ignorant people don't seem to realize. 

Sounds like the frame is trashed.

I'll pick it up and dispose of it for you in an environmental way.

Might as well leave the components on it too, those will be no good now. 

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