General Cycling Discussion - Mysterious Blowout
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07-15-07, 04:47 AM
I was grinding up a hill on my fixed gear commuter when the rear wheel went wobbly for about two revolutions, then the tube exploded. It has been pumped up to 110 psi, which is a little higher than usual but certainly not a first on that wheel/tire combination. Furthermore, I had not changed the tire or tube for nearly a year (at least 600 miles), so something should have happened earlier if the tube was installed incorrectly back then. When I later took out the tire for inspection, I could find no defects --- there were several nicks from debris but none that cut right through the casing, the bead seemed fine, etc. Just to be safe I bought a new tire anyway and got home (approx 12 miles) on it without incident. I also checked the wheel and it had an almost unnoticeable wobble, not enough (I would think) to cause the blowout. The hole on the tube was slightly off-center.
The tire was a 700x23 Vredestein Fortezza SE (rated to 160 psi), mounted on an IRO rim. I can't find any indication of pressure rating for the rim, but I would be surprised if they were rated to less than 110 psi.
Any thoughts on what could have caused the blowout?
07-15-07, 05:06 AM
Assuming no thorn or glass shard caused your flat, there is always the possibility the tube had a weak spot that finally gave out. Some people have reported flats due to poor quality rim tape. Velox tape is recommended as the best. I am assuming your rim is double walled so that no spoke tips come in contact with the tire, as on older bikes from the 1960s, etc. Sometimes the bead slips away from the rim and the tube explodes without the support from the tire structure, but that is usually very soon after installation of a new tube or tire. I am assuming there is no place where the rim is bent on one side and the bead does not grasp the rim properly. There may have been a fold in the tube that pinched the tube and in time it wore through. I had a problem once with gradual air loss in a tube and inflated it with the aerosol fix-a-flat stuff for automobiles. Bad idea! After just a couple of miles something happened and the tube exploded so violently that the rim was permanently distorted too much to make true ever. Another time I inserted tire liners to protect against nasty thorns. The liner would not stay in place, so I used a small piece of duct tape to hold it. Another bad idea! The adhesive turned gooey after a few months and etched through enough of the tube that the tube broke open with a heavy leak and I barely made it home, even after stopping several times to pump air into the leaking tube. If you have tire liners installed, they sometimes pinch the tube and cause a flat. I have also had a couple of flats with presumably logical explanations, but I never determined what they might be.
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