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I have had two innertubes explode on me on my bicycle, on the same wheel and tire. The first time I was inflating my inner tube after aquiring a puncture. On this occassion I was pumping my tires (rated at 50-90psi) beyond 70psi.

After the first explosion I replaced the innertube, being careful to avoid pinching. I pumped up to 60psi. A few days later the inner tube exploded while the bike was hanging on it's rack.

After becoming the recipient of yet another puncture on the same tire (city streets...), I am wary of my inner tube installation. This time I inserted the inner tube under the tire, moved the tire beed back to the inner rim, and carefully checked to ensure that no pinching occurred. I have now inflated the tire to 60psi.

My concern is that, despite being very careful, I have sections where beed appears to be showing. My question is, given the amount of bead showing (about 2mm in one section), could the inflation cause another inner tube burst?

Bead! Bead?

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How did the punctures occur? –  Batman Apr 6 at 23:12
    
They appear to be routine punctures. Both times I found small holes, at different locations (implying that there isn't a persistent puncture at one point on the tire. –  MM. Apr 7 at 0:22
    
Any bead showing is too much. It's meant to be inside the rim. –  andy256 Apr 7 at 0:31
    
How does one keep it inside the rim? –  MM. Apr 7 at 0:50
    
Actually, I may have misinterpreted what the bead actually is. I am assuming the bead is everything inside of the inner ridge, visible in the picture (there are vertical lines on the inside of the ridge). Please let me know if this is the case. –  MM. Apr 7 at 2:40

3 Answers 3

up vote 3 down vote accepted

The visible strip sticking out from the top of the rim and inside the line is in fact the Chafer strip. This is on the tire to prevent the bead hook on the rim from cutting into the tire.

The bead is the wire or in the case of folding tire such as the x'plor ush Kevlar ring on the edge of each tire. When seating the tire the bead is place inside the bead hook on the rim with a tube inside.

Rims have a few different standards and many proprietary designs so do not have a consistent inner sidewall height. The tire bead when seated actually sits at the bottom of the rim rather than on the hook, so the amount of Chafer strip shown is dependent on the depth of the rim.

The amount of Chafer strip showing would not be a cause of your tube exploding and there are many answers that address punctures but my thought would be something loose in the tire.

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Based on your edit, do this. Remove the wheel, deflate to about 10 PSI, then roll it along the ground, pressing down hard, for several revolutions.

After you've done this examine the strip. Anywhere where the strip is not showing the "average" amount, tug on the tire to pull it out. Anywhere where the strip is showing too much, first examine the opposite side of the tire at that (ie, the left side of the tire if the problem's on the right). If the strip is not showing as much on that side, tug it out a bit. If the strip is showing too much on both sides try to work it inward (tug out other places where it's too close).

You may find that the tire sits too high near the valve. This is often due to the thick portion of the tube near the valve being caught between the bead and the rim. In that case, push the valve into the tire (remove the nut if there is one) and try to rock the tire back and forth to get the tube in the right place.

You may find a spot where the tire sits too low. This can be due to having twisted the tube while installing it.

Once you've got the tire relatively well centered, inflate in increments of 20 pounds or so, roll along the ground, and inspect/align again, until you reach your desired pressure.

And, of course, if you have a blowout on a tire, always examine it for actual holes that will let the tube "balloon" through. Small ones can be fixed, at least temporarily, with a "boot". Bigger ones (larger than about 1/4") would require the tire to be immediately replaced.

And, since you don't say what size this is, remember that not all 26" tires have the same rim diameter. Make sure that the metric diameter on your tire matches the metric diameter of the rim.

Also, when installing a tube the way to do it is to first inflate the tube just enough so that it rounds out and limply holds its shape. Then work the valve into the valve hole and tuck the tube into place. This is easier than inserting while completely flat, and it helps assure that the tube is not twisted or caught between tire and rim.

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As far as I know, the line that you are seeing is indeed an indicator if the tire is properly installed. It doesn't matter how much it is showing. What is important is that it is visible.

If the indicator is showing too much somewhere, it will be hidden under the rim on the opposite side of the rim (opposite passing through the diameter). This would be an indication that the tire is seated in a wrong way and may:

  • fall out under pressure when cornering
  • give a rough ride.

Or I think this is how things are supposed to work.

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1  
While the line can be used to see if a tire is seated equally around the tire it actually is a strip of rubber that is reinforced to prevent chafing between the tire sidewall and the rim bead hook. It's called a chafer strip and you'll find it on every type of tire. –  DWGKNZ Apr 7 at 10:44

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