I'm not even going to venture what caused this one. The tube in question has been in since February and probably has well over 1k miles on it, but it decided not to play anymore today.

I was on a mup when it happened, and I had just passed a couple walking. Since it sounded like a small caliber round going off, the sound scared the jabbers out of the poor couple.

True blowouts like you describe are hardly ever the fault of a tube - it's the tire or the mounting of the tire, too much braking on a hot downhill, or once in a while the rim. A bad tube will just go flat without an explosion.

You trapped the tube under the tire when you mounted it. It eventually lifted the tire and blew out between the tire and rim.

When you install a tire and tube, the tube must be inflated until it is round, throughout the mounting process. After the tire is on the rim, go around on both sides, pushing the tire bead inward and looking to make certain that you can't see the tube anywhere. Then pump up the tire. After pumping, look at the tire on both sides and see that it seems evenly mounted.

I once had a tire pump that read about 25 lbs low on the gauge. In other words I'd inflate to an indicated 120 psi and it actually had more like 145 psi in the tire. While it never caused a blowout, I could see where such an improper pressure reading could.

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+1 . This happened to me about one month ago when I replace the inner tube at home . The bang was so loud I though there goes my hearing at 56 .

What does your tire look like?

I'd agree the most likely cause is trapping a fold of inner tube under the tire bead. If your tire doesn't look damaged, that's almost surely it.

If your tire has circular marks just adjacent to the rim, check your brake pad alignment. If your brake pad touches your tire it will wear through and eventually blow out.

Could have been heat. Hear them explode all the time in the pass thru towns on Ragbrai. Inflate a tire to maximum pressure, ride twenty miles on hot asphalt, sit down and wait for bang.

+1 Blowouts are are rare unless there is a mounting error. I have only had 2 in over 40 years of riding and they were my fault; too much tire pressure and the tire popped off the rim, and a "heat related injury".

When I was racing, we went up to Seattle for a race on one of the nearby islands. We arrived early the night before, so I thought I'd get my bike ready, including pumping up my tires. My sew-up tires used 120 psi for best results. I pumped up my tires and wheeled my bike into the motel room and leaned it against the wall, fairly close to the heater. About midnight there was a loud explosion as my front tire reached the bursting point.

While the other guys enjoyed an early breakfast on the ferry ride over to the island, I was down on the car deck(in February) patching my only spare tubular tire. It all worked out.

Well, since this has taken a turn to why I had another blowout, instead the humorous way I scared the crap out of the poor couple walking, I'm pretty sure it's tire related.

The reason I'm leaning that way is I've been riding LBS bikes since I was 14, and in all that time I've never had a blowout until this summer. So while I'm not saying I'm perfect installing tires and tubes, I doubt I pinched two blowout causing tubes

Even though I said I wouldn't even venture a guess as to what caused this one, I know what caused it and it was a cut on the tube. My guess is the new tires (Vittoria Rubino Pro's) I put on the bike in March have a sharp edge on the inside of the bead, and when I put my new tube in, I'll pull the other tire off, and give them both a shot of sandpaper on the inside of the bead.

I would imagine that'll be problem solved.

I'm sorry, I did not see the humor in that.

Sorry, I guess I should have mentioned we all had a good laugh about it. They did ask what happened and if I was ok.