One of my tyres had gradually deflated during my 2 week absence so I decided to change the tube
before riding. As I pumped up the tyre there was a loud bang as the tube exploded. About 8" from the
valve there was a little bubble of shredded tube peeping out between the rim and the tyre. When this
happens it is usually a result of incompetent tyre fitting - the tube is sitting under the bead and
lifts it off the rim as it is inflated. Once it is able to peep through a bubble forms with the
inevitable result. So I put another tube in, made trebly sure the tyre was correctly seated with no
tube visible anywhere under the bead, pumped it up, put the wheel back on the bike, and moments
later got an even louder bang. The pressure in the tyre was 120 psi; the previous bang had occurred
while pumping at around 80 psi. This time too the bubble had retreated back into the tyre and was no
longer visible although clearly part of the tube must have been outside the tyre for it to go bang.
When I fished this tube out it was clear that the burst had occurred in exactly the same position as
before. Inspecting the 700 x 23C Hutchinson Gold folding tyre more closely it was apparent that the
bead was slightly soft at this point. Although there was no obvious tear or break, the tyre formed a
distinct crease at one spot when flexed.
I suspect that the first explosion was due to my not fitting the tube correctly, and that did the
damage to the bead, making the second bang inevitable. Although the damage was probably my fault it
does appear that the beads of these tyres are quite delicate. It was fortunate that it happened at
home rather than at the side of the road.
Another curious thing is that the original tube, the one with the suspected slow leak, seems to be
perfect. I've no idea why it went down.
--
Dave...