Originally Posted by
dddd
On narrower tubes, the reinforced rubber pad surrounding the valve stem goes about half way around the tube, and hardly stretches at all. So as the narrow tube expands to fill the volume of the larger tire, half as much rubber ends up having to do all the stretching needed for the tube to inflate to the tire's cross-sectional diameter, which is apparently enough to cause any additional stress concentration (such as a seam, or at the pad's periphery) to perforate.
If the perforation is indeed facing the rim channel, then the pad surrounding the valve stem never settled into the rim channel, so on an older tube there will be tell-tale stretch marks in the thinner rubber evident there.
Interesting ... it looks like the puncture was actually more like 135° from the valve ... I'm not sure my tube has the narrow strip you mention. The hole was was closely adjacent to the seam if not on the seam.
Originally Posted by
jimmuller
Is that finger-cross thing 3x or 4x?
I've seen defective tubes.
You said 90deg from the valve. Does that mean around the wheel or on the side of the tube? The latter may indicate a pinch hole from when you squeezed the tire on the rim. Tire irons can be deadly to tubes.
It means around the rim ... picture should explain, actually closer to 135° by my estimation. I use the yellow plastic Pedro's levers and try to be careful (perhaps not careful enough ...).
Originally Posted by
T-Mar
Or maybe, during installation, the tube was was pinched between the tyre bead and rim, causing the puncture. The puncture would be sealed by the pressure of the rim and tyre bead, until the tube slipped out from under the bead, at which point it would quickly deflate.
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This seems plausible as well.