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Just how brittle are carbon frames?

rockhopper70rockhopper70 Posts: 36
edited January 2011 in Workshop
I have a "friend" who came off a carbon framed bike. No obvious signs of damage but advised that the frame should be scrapped in case it has been weakened and could fail catastrophically without warning. So...every time a carbon bike is dropped the rider needs to buy a new frame? That can't be right can it. Surely it has some degree of resitance to impact. Would there be any tell tale marks on a carbon frame to show any excessive stresses on it?


  • Monty DogMonty Dog Posts: 20,614
    My first thoughts were that Cannondale video. Unless the frame is showing visual signs of damage, I'd carry on - the likelihood of sudden and catastrophic failure is unlikely. By all means get an experienced mechanic to look at it - but not the one who suggested it needs replacing! I've been riding a carbon frame for three years that was involved in a rear-end shut with a Disco and has two cracks - one on the toptube and the other on the downtube - it didn't cost me much and doesn't owe me anything. I've marked the cracks with a marker pen and so can easily see if they're going anywhere.
    Make mine an Italian, with Campagnolo on the side..
  • I suppose it depends on how severe the crash is, on a 30 mph prang and the bike goes end over end several times that might be a case of a new frame especially if there is visible damage, but most crashes are slower and the bike usually just slides on one side,i had one like this on my CR1 two years ago, didnt touch the frame, the rear mech and shifters took the impact, checked the frame for cracks but found nothing so just carried on riding with no problems since.
  • topdudetopdude Posts: 1,557
    I don't ride a carbon framed bike but i did an experiment with an offcut from a carbon steerer tube.
    I clamped it in a vice and tried to crush it across it's diameter (you have to do these things) :D
    It took a lot of force to deform it to an oval shape and i kept going until the inside surface started to delaminate a little.
    When released it just returned to it's original shape, try that with Alloy or Steel and it would end up just a bit of flat metal :wink:
    I doubt this would work with a much thinner section of frame tubing but it was impressive that the carbon didn't just explode in small pieces.

    The funny thing is that people feel compelled to buy a carbon frame and then are terrified of the slightest scratch or bump in case it breaks. It is some tough stuff but if you don't trust carbon then don't buy it :?
    He is not the messiah, he is a very naughty boy !!
  • moonshinemoonshine Posts: 1,021
    get it ultrasonically tested? that should show up any materials flaws,
    I don't know too much about it in practice, but my good mate is a consulting nuclear engineer and metallurgist and has access to one. He said it will show up flaws in all materials (metals, inc welds and composites inc. carbon materials).
  • Unless you have access to (expensive) ultrasonic testing there isn't anyway to tell if CF is damaged or not - that is the issue.
  • geebee2geebee2 Posts: 248
    Unlikely to have damaged the frame in a normal off, unless the frame collided with some object.

    By "normal" I mean say losing back wheel on greasy surface and ending up sliding along road.
  • WappygixerWappygixer Posts: 1,396
    I've just had a frame returned to me for instection.Its a full carbon frame which to most looks ok.
    On closer inspection though the top tube has a crack going along the length for about 8cm.After a few mins trying to decide how it happened we noticed that it lined up with the handlebars and stem.We think when the bike crashed the bars went full lock and that impact cracked the frame.
    It all depends how you crash really.
    A slow crash where you end up on top of the bike could be worse than a 40mph downhill crash where the bike just slides.

    A guy at work had a head on on his alloy frame/carbon fork road bike.The fork look nigh on perfect but the frame broke away at the headtube, clean off
  • markos1963markos1963 Posts: 3,724
    I can't believe this still comes up so often. The airline industry,anglers, F1 and all sorts have been using CF for donkeys years. Any crash may write off any frame material, as others have said it's the nature of the crash which determines the damage. A mate of mine had a massive crash in front of me at a crit last year, his Felt F1sl was completely fine.
  • Evil LaughEvil Laugh Posts: 1,412
    Check this dude out. Whacking the crud out of a 500g carbon wheel, w carbon spokes. ... re=related
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