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I found a crack underneath the handlebar. Is it okay to keep using it? I can't really afford a new one. I'm riding with the cracked bar right now and there's no weird sound and movement on the handlebar.

To make things easier to explain, here is the crack

enter image description here

Not sure what happened. I can feel the crack with my hands and I felt a string like material on the crack. I lent my bike to my brother and he came back with a broken bike. I replaced the broke parts and I didn't check the handlebar until when my friend noticed a strange white line under the bar. I already know it needs replacement immediately.

Please tell me what cause the crack so I might avoid the same problem again in the future.

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  • It's unclear where this crack is. And be sure you know the difference between a crack and a simple seam left in the piece from manufacturing. – Daniel R Hicks Sep 15 '18 at 11:40
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    The underside of the handlebar or stem is a strange place for a crack to develop, the material there is under compression rather than tension. If there is a dent there may have been an impact. Is this on an MTB? Did you crash? Adding a well lit photo to you question will really help us help you. – Argenti Apparatus Sep 15 '18 at 11:51
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    That appears to be a carbon bar (which is quite rare). All bets are off. – Daniel R Hicks Sep 16 '18 at 1:15
  • Sounds like your brother does not care for other people's stuff. Don't loan him any more bikes. That will avoid this exact problem happening again. – Criggie♦ Sep 16 '18 at 1:31
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Yep. That CF handlebar is trash. A dent or indentation, or loose carbon fibers that are free of the epoxy matrix indicate carbon fiber composite it is seriously damaged and weakened.

You know how this got damaged. Your brother crashed your bike. End of the bar hit the ground, bar broke. Simple as that.

BTW, it doesn't matter that you can't afford to replace broken components because your brother owes you and should pay for the damage.

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    i once told him about the crack he changed the topic. – Lam Munn Juan Sep 16 '18 at 6:56
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DON’T

If you are sure (or have strong suspicions) it’s a crack and not just a scratch, stop riding it.

From your description I’m not sure what’s actually cracked (stem, fork’s steerer tube, frame’s head tube?) but replacing it is much cheaper and less painful than new teeth or sitting in a wheelchair the rest of your life.

Post a picture if you want a more accurate assessment but generally the only components on a bicycle where I’d be okay with imminent failure is anything related to gear shifting or attachments such as bottle cages or mud guards.

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  • I'm sure its a crack it is on where i install my shifter & brakes i can feel a dent on it too. Okay, ill stop riding riding it for now. – Lam Munn Juan Sep 15 '18 at 8:06
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    Ah, so it’s the handlebar? You can get a new one for 10 or 20€. Stems are also quite cheap. Only frames and forks are more expensive. – Michael Sep 15 '18 at 8:33
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If the crack is in the handle bar, the failure mode is as follows:

  • One side of the handle bar breaks off.

  • You fall forward, one hand pushing the broken off handle, the other hand pushing the still connected handle.

  • This falling motion will steer your bike sharply to the side with the broken off handle, effectively kicking your bike out from underneath your butt.

  • You will make contact with the road at the full speed you were riding at.

The resulting damage depends on your exact speed and road conditions, but I've had this type of accident once at about 20 km/h on a smooth surface (no sharp edges or bumps from tree roots, uneven sidewalk tiles, and the like), and it's still the third most severe accident I've ever had.

Note that the energy that goes into bruising you will go up with the square of your speed. So, at 30 km/h you have to expect more than twice the injuries than at 20 km/h. Do this at 40 km/h, and you'll have to hope that you are found before you bleed to death.

A crack in the stem itself may give a similar failure mode, or it may break directly forward. I don't know what would happen in this case, but my intuition tells me that this would be much more dangerous than falling sideways at full speed.

Bottom line: Your fork, your stem, your handlebar, and your steering tube are too critical for your security to ignore cracks. If any of these fail, there is no backup, and the failure modes are scary. You won't have any chance of mitigating the consequences of the crash.

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  • This perfectly describes what happened to me, I was going at low speed, just pulling off from some lights. But it threw me across the road, and if there had been any traffic I would have gone under it. – stib Sep 15 '18 at 23:30

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