Why did my bicycle tire explode?

Factual Questions
1

I rode my bicycle to work yesterday, as I do every day, and as I’m sitting at my desk I hear this creaking noise behind me. I turn around, and it’s coming from my back tire. I get in close to it, and I can see that the tire is actually being pushed off of the rim from the inside, and the tube is starting to show. It pushes more and more of the tire off, and then all of a sudden the tube pushes completely out the side of the tire and off the rim, so it’s kind of hanging off the side of the wheel in one place. and it’s still growing! The tube is expanding, all by itself, getting bigger by the second, growing this bubble about the size of a grapefruit. All of a sudden BOOM! It pops! It popped all by itself! How did that happen?

Some more info: It was pretty cold outside, around 45°, and probably 65° in my office. I wouldn’t think that was enough of a differential to cause such a drastic reaction, especially as the tires were probably warm from the ride. And the tube wasn’t infalted anywhere near the maximum pressure for the tire.

A friend and I were speculating that maybe there was a weak spot in the tube that allowed the pressure to push it out just a little bit, which weakened it more, allowing more of a bulge. We figured maybe with a small difference in the radius of the tube at that spot that the pressure inside could have been focused at that point, thus making it worse and worse. Is this possible? Are there any other ways this could have happened?

Any answers are greatly appreciated.

2

Probably the bead cable broke. There’s a steel cable embedded in the rubber around the bead, where the tire is seated on the rim. The cable probvides structural tension to keep the tire firmly seated under pressure. If this cable (there are two, one on either side) snaps, then what you saw is the inevitable result. I can only speculate on why it might have snapped in the first place, though. Perhaps the cold made the metal brittle at a weak spot, and a hard bump caused it to break.

3

What kind of tires and rims are these?

Are they “hook and bead” or are they the old-school straight-sided rims? If the latter, it’s really easy to not install the tire correctly and have exactly this type of failure occur.

4

I second that emotion.

Is the side of the tire that let the tube bulge out looser than the other side?

5

As far as I can tell, the tire’s pretty even all the way around. I put a new tube in it and it seems fine, but I’ll have to wait until I get home tonight to take it off and check.

6

Have you had a puncture recently? If so, maybe you didn’y mount the tire correctly and it’s been working itself loose. When it evventually pops off the rim, the inner tube explodes.