tube bulging out where stem meets rim

Discussion in 'Cycling Equipment' started by geardad, May 10, 2008.

  1. geardad

    geardad New Member

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    I've got a tire I've been riding on since I put the tire on: an armadillo and a (then) brand-new tube. Schraeder valve.

    worked out great..those armadilloes worth everypenny.

    lately, noticed bulging of the tube where the stem emerges from the rim.

    anyone know why this would happen? the hole in the rim is sized for schraeder, not presta.

    just an old tube?

    thanks!

    gd
     
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  2. Aussie Steve

    Aussie Steve New Member

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    I'd be cautious about this as there is potential for explosive blow-out; you may want to change the tube for a brand new one. Also check the rim tape. What i do, is put some duct tape around the valve-hole in the rim...just to protect the part of the tube directly around the base of the valve...
     
  3. lohsnest

    lohsnest New Member

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    A few times, I have noticed similar situations with my tires... I discovered that with my clinchers, the tube's valve fits into the hole, but is an extremely tight fit. You have to be very careful to ensure that the tires are installed properly. The bulge on my tires turned out to be a pinched tube...the tube was not installed properly and was being pushed against the beading of the tire and the inside wall of the rim.

     
  4. oldbobcat

    oldbobcat Well-Known Member

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    Let me get this straight. You've got a Schraeder valve and a rim drilled for a Schraeder valve.

    Is the bulge coming out the valve hole or is it at the tire casing where it seats on the rim. If it's the tire casing, release most of the air pressure, push the valve stem into the tire to ensure that the tube is inside the tire and not pinched between the bead and the rim. On narrow tubes, the hard rubber surrounding the stem can cause the tube to get pinched here. As you re-inflate slowly, check that the tire is correctly seated on the rim.
     
  5. geardad

    geardad New Member

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    you got it straight, oldbobcat.

    this tube/tire combo had been mounted for about 18 months, yet only recently this bulge popped thru...pretty amazing, too, since there's very little clearance in between the rim metal where the valve stem hole is, and the valve stem itself.

    I did end up letting out most of the pressure, then replaced the tube, destroying the old tube by cutting the valve portion of the tube out with a pair of scissors..

    when I inspected the valve area of the tube which had the bulge (after cutting the valve out) it appeared to me that there were 2 layers of rubber around the valve, and that air pressure had "sneaked" between the 2 layers, and managed to pass 2 walls of rim metal, through tight clearance, to pop out the other side and form this bulge.

    pretty impressive display of what 100 psi can do, eh!?


    thanks!

    geardad
     
  6. oldbobcat

    oldbobcat Well-Known Member

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    Think I've had that happen once or twice, but the tube was a lot older than 18 months, but I've never had occasion to pump a Schraeder-tubed tire higher than 85 psi.

    Goes to show--if you have to scrape the tube off the rim, it's time to replace it.
     
  7. geardad

    geardad New Member

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    couple other things that might factor in...the tube which did the bulging, when I pulled it off, felt markedly heavier than yer average tube. when I cut the valve out (to prevent future accidental use) the wall of the tube was 2-4 times thicker than normal. I didn't see any markings on the tube which would help explain this extra beefiness, and I don't recall asking for a beefier tube (tho I might have) but that even more makes ya wonder why the bulge; if tube is beefier, more resistant to bulges?

    also, the tire's rated at 100psi max; does that mean the tube inside can handle that as well? I don't see tube ratings for PSI or BAR pressures.

    gd
     
  8. kdelong

    kdelong Well-Known Member

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    Thicker tubes are a little more puncture resistant. The LBS Tech may have thought he was doing you a favor by using the thick tube. The thickness of a tube is not going to be more or less prone to bulging. The scenario that you have described is possible, regardless of the thickness of the tube.

    Any tube inside of a tire will hold air up to the maximum inflation pressure of the tire as the relatively thin tube material is being backed up by the stronger, thicker material of the tire. Usually the tire will fail before the tube does. A tube only pops when you infate it outside of the tire and it expands to the point where the rubber splits. If your tube fails before the tire, then you have a mismatched set up of rim, tube, and tire. The one exception to this is when you have a defect in the stem area which is pushed out through the stem hole of the rim by the internal pressure.
     
  9. cyclemanx

    cyclemanx New Member

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    The tube is bonded to the metal valve stem, but air pressure can break the bond until the stem becomes totally detached. It happened to me once when I was pumping up a brand new tube. The shop was happy to give me another tube.
     
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