Join Date: Dec 2004
Location: Middle of da Mitten
Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, homebuilt recumbent
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What you're describing is a blowout, and since the tire being ripped to shreds isn't part of the description, then what you likely have is a pinched tube due to improper installation. ClosedOffice had it almost right; except the tube doesn't 'work its way out,' the uneven bead is caused by the tube already being between the tire and rim. For some reason, tubes trapped that way never work their way back into the tire, sooner or later they always escape. And when they escape, POW! So, here's what to do to avoid it in the future:
First, mount the tube and tire. Then inflate the tire to 5 psi or so. Now, working your way around both sides of the rim, push the tire's bead away from the rim. if the tube is 'pinched' there between bead and rim, the small amount of pressure in the tube will cause the tube to return to its intended toroidal shape inside the tire's carcass. When you're done working your way around both sides, spin the wheel and observe that the 'witness line' is even along all points of the rim. Then it's safe to pump up to full pressure.
This past summer, a friend got a new bike and was plagued by blowouts. The shop kept replacing both tubes and tires under warranty, to no avail. After about a dozen interrupted rides, I finally grabbed the wheel from him and performed the procedure above. He hasn't have another flat since. The moral is, even shops can screw up mounting tires.