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Had a puncture today, removed the tube, patched it and made it home. Obviously since I only have a mini-pump I could not inflate it to my 8 bar usual pressure.

When home, I took the wheel upstairs to inflate it with my big pump. Inflated it to 8 bar and put the tire aside to mount it on the bike tomorrow.

A couple of minutes later: BANG and when I looked, I saw this:

enter image description here enter image description here

Seems like the tube exploded (not exactly around the valve but not far from it: you can see the cap on the far right in the second pic) and blew off the "clich" part of the rim.

What could have caused this? the tire is a Conti 4S that can handle 8 bar, the tube is a Schwalbe standard tube that does support 700x23 dimension. The rim was a Mavic Open Pro...

Sucks,... did not feel like buying a new wheel now :(

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What is that black strip hanging down? Is that the tire's bead? –  Daniel R Hicks May 23 '13 at 21:52
    
No, it is the rim, the top of it. You can see the start of the tear on the right (2nd picture), under the 3rd "n" of "Continental", and you can see the shiny strip of torn away metal. –  tisek May 23 '13 at 22:21
    
Unusual rim. Is that solid metal or part plastic or what? Anyway, the rim failure was what precipitated the tire failure, presumably. –  Daniel R Hicks May 23 '13 at 23:25
    
It surely is metal. Not saying it is supposed to be a fatastic rim but it is a Mavic Open Pro, so it is "serious" stuff. Anyway, will take the whole thing to my LBS who'll build me a new wheel with a new rim and my hub and cassette, hope my tyre is ok... –  tisek May 23 '13 at 23:39
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Minor note: Probably the stress of levering the tire off/onto the rim caused a crack that precipitated the failure in this rim that was apparently already weakened due to wear. The rim would have failed eventually -- the tire change made it happen when it did. –  Daniel R Hicks May 25 '13 at 11:57
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3 Answers 3

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The tube does not contain the pressure. Consider what happens to a tube is you put 8bar into while not mounted inside a wheel+tire...... If the tire cannot contain the pressure, the tube explodes, but it is that lack of conatainment that causes it.

Problem is the tire or the rim. This cna be caused by :

  1. Tire / rim mismatch
  2. Rim Faultly
  3. Tire faulty
  4. Tire incorrectly installed

We know its not 1). Have a look at the rim and check for faults and damage. Then inspect the tire for a faulty bead or tear. It may not be visible (A broken bead can be hard to see but can usually be felt.).

In your case, it looks like the bead has separated and you need a new tire.

Another likely cause in my mind is incorrect mounting. Install a new tube, pump it up, let it down and pump it up again to full pressure - all the time watching whats happening to the shape of the tire. Any sign of deformity, you need to investigate.

Edit: Information provided in the OPs comments indicate the rim has failed rather catastrophically (Fault 2. in the list) - I incorrectly assumed the strip was off the tire. You have a coice - if you don't want to buy a new wheel (at least rim, but a made up wheel is often cheaper) you don't have to - you just won't be able to ride the bike... I suspect what happened is the the rim was damaged by either riding with the puncture or during the repair, and has developed a crack. The stress from the ire pressure was too much for it. Another possibility is you put more pressure into the tire than the rim is rated for - however they should handle 8bar.

I would strongly recommend a new tire and tube for the replacement rim........

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I like to inflate the tire a bit, then let it down nearly flat and take it and roll it along the ground a few revs while pressing down a bit, to kind of center and seat the tire bead. –  Daniel R Hicks May 23 '13 at 21:54
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This kind of failure is typically caused by excessive wear on the brake surface of the rim.

Every time you apply your brakes, you are polishing small amounts of metal away from the rim. Eventually, the rim gets too thin and weak, and will crack, like you have seen in your photo, from the normal inflation pressure of the tire.

In general, this means tht the rim has been used beyond its life. If it is a new, or lightly used rim, it may be a manufacturing defect.

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Good thing you were not riding when the rim blew out! As others have said, brakes wear down the sidewalls of wheels. I'd be surprised if there were any other cause of the OP's rim failure. Some of my wheels have a WEAR indicator on the wheel which is just a 'radial' grove in the wheel. When that grove starts to disappear, time to throw away the rim and put on a new one. I inspect my wheels at least a couple of times a year.

This problem is rather well documented and known. Do a google search on "bicycle rim wear indicator" to see examples of the OP's problem.

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