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  1. #1
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    Potential crack on a top tube?

    Hello fellow 2 wheelers. I got a CUBE Reaction GTC frame. I was working on it few days ago, and I've placed it in a bike stand. I know that the top tube is never to be clamped down, so i warp it up in bubble wrap for protection, and close the clamp just so that the frame doesn't fall out. No pressure. I did that a few times before, and on several other bikes with no problem. Today, there was a problem. Either my clamp was set a bit narrower from other frames, or something else.. but while I started to press down the clamp ( I repeat, the pressure is minute) i heard a slight crack. I immediately took the bike out, and inspected the top tube, but saw nothing. Now, there is a visible mold line from the day I bought the bike.. and As I press the top section of the tube... it flexes a lot, and I heard a few cracks more. There is no visible crack on the outside, you can't feel anything under your fingers, but I have a feeling that the UD carbon beneath the cosmetic top weave has came apart on that same mold line. I contacted my LBS, and a local dealer, as well read some forums, and I get mixed answers. Cube dealer says that he can flex every CUBE carbon frame he has in the shop, since that is the thinnest part of the frame. Some german user sent the frame back for inspection, after hearing a slight crack while sitting on the top tube, the factory returned it and said that all stress testes were performed, and the results are in green. I've also contacted a local frame repair shop and got a reply not to touch anything, nor to be overly concerned. The tube is never under pressure perpendicular, but lateral. If I ever notice a crack appearing, then have it repaired.
    I ride XC, sometimes race, mostly a weekend XC warrior. I'm a big guy, 220lbs, and although all of them assure me i'm fine.. I can't stop worrying about possible frame failure during rides. I'm attaching a video, and a coin test.. so I could get your opinion . While filming this video.. try as I might, I couldn't get my finger to split the carbon...

    https://www.youtube.com/watch?v=v-9vL892Rp4
    https://www.youtube.com/watch?v=VcWf6C1VSys
    https://www.youtube.com/watch?v=3OPcH1nujOs

  2. #2
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    I sure don't know much about carbon bikes, I'm a steel or Ti only type of guy, but that would scare the crap out of me too.
    Sorry I can't be of more help.
    I am going to watch this thread though, as I had a pipe dream recently that involved a carbon frame.

  3. #3
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    I'm sending it out to a carbon shop next week, just for them to open it up, and put a fresh layer of carbon on top...

  4. #4
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    Quote Originally Posted by Hodo View Post
    That would scare the crap out of me too.
    Sorry I can't be of more help.
    This...glad you're doing something about it.

    Also, I know it's not supposed to be, but I found this part funny:

    "after hearing a slight crack while sitting on the top tube, the factory returned it and said that all stress testes were performed, and the results are in green".

    Glad your German stress testes results came back green. Wait, what?

  5. #5
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    Quote Originally Posted by ChILd_ReBoRn View Post
    I'm sending it out to a carbon shop next week, just for them to open it up, and put a fresh layer of carbon on top...

    That's kind of overboard, I'd have it x-ray'd first.

  6. #6
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    You wouldn't catch me throwing a leg over that frame. I've seen blocks of cheese that exhibit less deflection. I can't imagine that all Cube frames are that soft, as the Cube dealer claims.

  7. #7
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    Quote Originally Posted by thesmokingman View Post
    That's kind of overboard, I'd have it x-ray'd first.
    Right. That would be okay If I didn't live in a country where people wait months to get x-rays in a hospital. I deeply doubt that someone even does x-rays on frames here..

    On the other hand, I heard a crack. There for something gave. Its a 2 hour job to sand it down and stick a patch...

  8. #8
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    Quote Originally Posted by ChILd_ReBoRn View Post
    Right. That would be okay If I didn't live in a country where people wait months to get x-rays in a hospital. I deeply doubt that someone even does x-rays on frames here..

    On the other hand, I heard a crack. There for something gave. Its a 2 hour job to sand it down and stick a patch...
    You seem set on opening it up, but just in case its called x-ray inspection just another form of NDT.

  9. #9
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    not sure what an NDT is.. but yes..I'm set on opening it up. im 220 pounds, and I don't want to F*** the frame up even more. It 's possible that it'll never give in.. or it could give in on a 35 mph descend.. or 15 miles away from my car...either way.. it's not worth the 40$ for a patch repair...

  10. #10
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    I'll borrow an endoscopic camera, and I'll shove it down the tube from my HT if I'll be able.. just to see what's going on...

  11. #11
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    That is 100% a delamination. As in, the outer layer of carbon fabric has separated from the next one. While you can't see a crack on the outside, there may well be one on the layer of carbon underneath.

    Seen this kind of damage on windsurfing boards a lot, it usually happens due to impact or in areas that are stressed often, like under the footpads.

    I would too go and ask a repair guy to open it up. If the guy is good at his job it should be as good as new after the repair and you won't have to ride in fear.

    I don't know how everyone assured you it was fine, it's pretty obvious it's not.

  12. #12
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    nothing is ever fine when I'min question. Usually everything that can go wrong, does go wrong. I'm pretty sure that this isnt my fault, but just bad quality resin or something...

  13. #13
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    Quote Originally Posted by ChILd_ReBoRn View Post
    I'm pretty sure that this isnt my fault, but just bad quality resin or something...
    Sorry to point it out, but you clamped the top tube yourself. A clamp set too tight can do this damage. A carbon frame can take big loads, but they're not designed to handle big clamping forces. I've seen similar damage caused by people tightening the shifter or brake bolts on their handlebars too tight.

    The bright side is that it can be repaired and it shouldn't be too costly.

  14. #14
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    I know I'm not innocent in all this.. but as I stated before.. my clamp is V shape, and the pressure exerted would be on the edges of the TT, not the middle, and the TT was wrapped in bubble wrap, so the V shape clamp pressed on the bubble wrap, and then on the frame.... again.. sides of the TT. But alas, it happened. As you said... it's not an overly big deal. I'm not planning to sell the bike any time soon ( just bought it) so I don't mind a bit of the aesthetic part...

    I took and endoscopic camera and shoved it inside. this is the picture:

    https://drive.google.com/open?id=1M3...aKL-XhJMcLzL63

    Bottom right part as the camera was really hard to maneuver in position. There is no crack or any torn fibers, but when I press on the outside the inside bulges irregularly. first a little bulge.. then another half a second later.. so there is something going on with the middle layer. It's off to repairs next week, and hopefully I'll have it back the weekend after...

  15. #15
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    Quote Originally Posted by ChILd_ReBoRn View Post
    I know that the top tube is never to be clamped down, so I......close the clamp....
    Um, OK.


    Quote Originally Posted by ChILd_ReBoRn View Post
    No pressure.....( I repeat, the pressure is minute)
    Ok, so which is it? None? A little bit? Perhaps more than you realize!
    That is why (see first quote!!) "I know that the top tube is never to be clamped down"

    Quote Originally Posted by ChILd_ReBoRn View Post
    Either my clamp was set a bit narrower from other frames, or something else....
    Thats why you never clamp down on a carbon frame tube!

    Quote Originally Posted by ChILd_ReBoRn View Post
    ....since that is the thinnest part of the frame.
    Hense the reason for never clamping, again.....





    Quote Originally Posted by ChILd_ReBoRn View Post
    I'm pretty sure that this isnt my fault, but just bad quality resin or something...
    Umm, see above.....
    "Go soothingly in the grease mud, as there lurks the skid demon"

  16. #16
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    I'm not a native English speaker.. so it sounds different when I make the sentence in my head . I did close the clamp, as in the lever that closes the clamp was in the position "close", but the nut that controls how far the jaws of the clamp get together was loosened up, so the clamp closes, but the jaws don't get to close to each other..

  17. #17
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    Usually when I see posts like this about carbon I look at the pics and come to the conclusion that the person is over reacting, but those 2 videos where you're pushing your thumb into the top tube are scary. I've got 3 Carbon frames as well as numerous Carbon bars and they just don't have soft spots like that.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

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