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Blowout after pumping up

Old 06-11-05, 09:38 PM
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ivan_yulaev
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Blowout after pumping up

So, I recently picked up a new bike for my dad. It's a Giant Cypress with 700x38 tires. I was pumping up the tubes to the max recommended pressure (85psi). Got them there, and let it sit. A few minutes later, the front tube exploded. When I took the tire off, it looks like a plain old blowout: 3 inch-long slit in the tube. Any idea what caused this? And should I take my LBS up on replacing the tube?
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Old 06-11-05, 09:50 PM
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Any chance you pinched the tube between the rim and tire? I assume you felt the rim and tire for any objects? Was the tube actually big enough for a 38? Maybe it was a 19-25?
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Old 06-11-05, 09:52 PM
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Well, the tire was fine at about 40 psi, so I didn't change anything. This was a brand new bike from the LBS, I just wanted to correct the pressure...
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Old 06-12-05, 02:27 AM
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Sounds like the tire bead was not seated. Check the tire bead and the rim seating surface for defects. Also check to see if the tire sidewall (especially near the tire bead) has a cut in it. Those are the 3 causes I have seen for the pump up blow out that you have described.
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Old 06-12-05, 08:10 AM
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The few blowouts I experienced during inflation were due to improper seating of the tire to the rim in the area around the valve stem. The tube construction at the valve stem is reinforced and the reinforcement could get between the tire bead and rim. To prevent this, when the tube is deflated, I push the valve stem into the tire and pull it out with my fingers. This forces the reinforcement away from the tire/rim interface and allows the tire to seat properly on the rim.

To this day, I'm always a bit shy when I'm pumping up tires. I always put in air (maybe 25% of full pressure) and spin the tire and observe the tire/rim interface. It's easy to spot potential problems.
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Old 06-12-05, 08:33 AM
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Originally Posted by MudPie
To this day, I'm always a bit shy when I'm pumping up tires. I always put in air (maybe 25% of full pressure) and spin the tire and observe the tire/rim interface. It's easy to spot potential problems.
I even go a step further . . . 'cuz we all learned the hard way . . .

At about 25% inflation, I go through the bead/rim interface, inch by inch, with both thumbs, pressing in and releasing the bead to insure it's fully and properly seated. I do this on both sides of the tire, then pump up.

Been pretty lucky so far.

Oh, yeah . . . and don't use those locking nuts on Presta valves. Too many people tighten them down too far and create just enough tear in the tube to . . . ruin your day.
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Old 06-12-05, 08:10 PM
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This made me remember when I was a kid and did not know about pumping up tires at the gas station. I thought the air stopped when the pressure was correct.

I was airing up my 24" Columbia and the tire exploaded. The old man lit into me for being stupid and killing my bike and having to call him to be rescued.

Joe
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Old 06-12-05, 08:21 PM
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Originally Posted by ivan_yulaev
So, I recently picked up a new bike for my dad. It's a Giant Cypress with 700x38 tires. I was pumping up the tubes to the max recommended pressure (85psi). Got them there, and let it sit. A few minutes later, the front tube exploded. When I took the tire off, it looks like a plain old blowout: 3 inch-long slit in the tube. Any idea what caused this? And should I take my LBS up on replacing the tube?
If the tube was installed with part of it between the rim and the tire, it would blow when being pumped up since the tire wouldn't be properly seated. This happens often around the valve stem area since that part of the tube is reinforced (thicker) around the valve stem, hence a little more difficult to seat. In the future, try this. Pump tire up to about 50 lbs. Spin wheel. If the tube isn't properly seated, the tire will be distorted in the area that it isn't seated properly. At this point, you would deflate the tire, push in on the tire in the area that's distorted to make sure the tube isn't caught between the rim and the tire. As to who's at fault in this case. If you installed the tube, it's on you. In very rare cases, where you get several blowouts, a defective tire or rim might be the cause.
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Old 06-12-05, 09:08 PM
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Well, went to the LBS. Excplained what had happened, they gave me a new tube. Put it in, pumped it up, everything is happy...
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Old 06-12-05, 09:43 PM
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Originally Posted by neil0502
I even go a step further . . . 'cuz we all learned the hard way . . .
I also try to pump it outside instead on in a garage. The times I blew a tube out (on both 120 psi road and 45 psi mountain) were indoors and the sound is literally deafening. In fact, you really don't hear the ka-pow it. All of a sudden, you hear this ringing and feel the air on your leg - and then I was frightened. Unfortunately, when you're pumping up, your ears are typically close to the wheel. If the tube blows outdoors, the sound pressure level should be less.

I just put on tube tire onto a tubeless rim, and the bead "snaps" into the rim as it's being inflated. I'd hear the snap and would jump. It snapped around 4 times, as the bead seated itself. Boy, I was a nervous wreck!
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Old 06-12-05, 10:22 PM
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One way to avoid blowouts due to improper seating is to partially inflate the tube before installing it. To do this, you should have the tire already partly on the wheel, with one of the beads on the rim and one off. Put just enough air into tube to give it some shape, then put the valve through the hole in the rim and tuck the rest of the tube into the tire and onto the rim. You can then put the other bead on the rim. Sometimes you'll need to deflate the tube again if it's a particularly tight fit, but this should allow you to get the tube onto the rim without pinching it or twisting it. The nice thing about this trick - not only is it easier to avoid a blowout, it's also much faster and easier than installing flat tube with the tire totally off the rim.

Most of you folks probably know this trick, but I thought I'd throw it out there, at least.
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