More proof that carbon breaks ...

Discussion in 'Bike buying advice' started by sitzmark, Mar 6, 2012.

  1. sitzmark

    sitzmark Member

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  2. davereo

    davereo Well-Known Member

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    Yeah. You may scratch it when hitting it against a stone wall./img/vbsmilies/smilies/biggrin.gif
     
  3. jpr95

    jpr95 Active Member

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    That first test was pretty much meaningless--it didn't mimic any real world conditions because the force was gradually applied over a long time.

    The second test, however, was very telling. 110 pounds impacting from 90cm (about 3 feet). So if I--at 190ish pounds--nosed in from 3 feet, I'm just about guaranteed to break that type of carbon (or aluminum) frame. That doesn't inspire a whole lot of confidence in those materials. I would have liked to see them also test steel and titanium...
     
  4. swampy1970

    swampy1970 Well-Known Member

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    I thought threads like this one died at the end of the last century.

    Becareful Sitz, you might fall over sideways if you let your leather toe strap gets a bit to chaffed and can't undo it in time. That said, if it gets too worn it'll snap. Have you made the change from 27x 1 1/4" tires to 700x25C yet?
     
  5. AlanG

    AlanG Member

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    Don't you think the fork would break or bend first? And the wheel would also deform and absorb some impact.
     
  6. davereo

    davereo Well-Known Member

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    That impact is roughly hitting a brick wall at 30 KPH. I would be worried about living never mind my frame. Regardless of frame material it is my opionion that if you ride the bike the way it is intended the frame will hold up to normal wear and tear. If Carbon fiber was a delicate material that was unsafe for bicyle frames manufacturers would stop using it to build bikes long before current owners would stop riding them.

    The test I would have liked to see was a repeat of the first two test after bashing the frame against the concrete. This would have proven if the integrity of the frame may have been compromised without breaking. With that information they could have shown if it is really a good idea to repair or reuse carbon after a crash.
     
  7. dhk2

    dhk2 Active Member

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    Cool video. Kudos to the Santa Cruz guys for allowing their destructive tests to be filmed. Certainly proves that the Santa Cruz CF frame is stronger and more impact resistant than the aluminum frame from the same maker. Of course, these test results don't indicate that all CF frames are stronger than all aluminum frames, but they ought to convince the nay-sayers who continue to bad-mouth CF that very strong and durable frames can be built of the material.

    Sitzmark, did I get something wrong here? If not, the video certainly contradicts your title and warning. The first CF frame went through a full 200K test cycle, plus two years of riding before it went into the load machine for the destructive test, where it still beat the aluminum frame. If that's not proof of the strength and durability of CF, don't know what is.
     
  8. alienator

    alienator Well-Known Member

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    The tests certainly show nothing of value. If the test is replicating hit a hill.....hmm....let's look at that. Let's say the rider and bike weigh 200lbs. Now, when they both hit that imaginary upside of a jump and generate the approximately 2000lbs of force that is required to snap the CF frame in the video, let's pretend that the bike and rider are locked together with super glue and that the rider's moment of inertia is exactamundo on top of the bike's and that their deceleration takes a laughably long 1 second....well, that means the bike and rider would've had to have been traveling at about 54.5 mph. Yup....and while all of that was going on it "Twas bryllyg, and ye slythy toves Did gyre and gymble in ye wabe..." It's about time, I guess, to re-watch those videos of guys driving trucks over metal and CF tubes.
     
  9. sitzmark

    sitzmark Member

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    Not something you can take too literal from a scientific standpoint – more comparative than anything. We don’t know to what load spec SantaCruz designed each frame; however, the two frames do have the same basic geometry and construction. Since SC doesn’t make this frameset in steel or Ti, there is no foundation to build any kind of relevant comparison around. That said, a similar frame could be constructed with thin-walled steel tubing which would fail far sooner than either of the frames in the vid. Material alone is not a guarantee.

    Technically I think both frames “toasted” fairly close together in the first test. The light reflecting off of the alu frame showed it began deforming around 850-900 (IIRC). That’s about the same force where the first carbon fiber “pop” happened. In both cases the integrity of the frame was compromised in some way at that point. The CF frame in the first test had been through 200k duty cycles in testing, then ridden for a couple of years, then subjected to this destructive testing. Contrary to a lot of preaching that I hear it still took a hell of a lot of force to make it fail. This was a well proven frame by a well respected manufacturer - other CF frames may or may not fair as well.

    Trying to extrapolate the results to real world is a crapshoot … suspension fork, inflated tire, non-fixed force vectors, etc. to dissipate the load. Just an interesting vid that shows CF can be pretty damn tough comparatively. At least for this SC frameset, “handle gingerly or your frame will break” does not apply.
     
  10. sitzmark

    sitzmark Member

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    Does 700x25C fit velocipedes? /img/vbsmilies/smilies/biggrin.gif
     
  11. sitzmark

    sitzmark Member

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    Obviously my sarcasm font wasn't working when I typed the title. /img/vbsmilies/smilies/biggrin.gif Agreed.
     
  12. dhk2

    dhk2 Active Member

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    Yeah, you got me! As Alienator's numbers show, the type of real-world impact needed to produce the failure load is severe....even for the extreme MTB crowd. Would be interesting if the video included a steel frame, as well as a road bike frame and fork.
     
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