Freakishly coincidental inner tube problem

I've just experienced two odd punctures. Firstly, I went to use my mountain bike and remembered the rear tyre had been flat for a few weeks. So I decided to fix it. It turned out to be exactly the same problem as what happened on my road bike last month. Coincidentally the Mountain bike tyre had gone flat at about the same time & also when sitting in the spare room, not on a ride.

Back in November, I went out and did a 120km ride. All was well, I got picked up by car where I was, delivered home. The tyre was good when I put it away. The next day, I went to clean the bike and to my surprise had a flat rear tyre. So I replaced the tube. When I looked at the old tube, I noticed a gaping hole on the outer edge of the reinforced bit where the valve enters the tube. I checked the rim tape & could see no reason for it. Put the new tube in, no problems ever since.

At the time I put it down to the tube being old...I'd done some 5000km without a flat since putting on some new Conti Gatorskin tyres and the tube had been inflated all that time. Rubber's degraded I thought...

So imagine my surprise today when looking at the old mountain bike tube to find exactly the same gaping hole at the outer edge of the reinforcement! Yes, it would also be a tube that had done long service, but I dont ride the mountain bike anywhere near as much as the road bike.

What's going on? Freakish coincidence or can someone suggest a reason for it?

It is the primary weak point of the tube and it is the spot that most mechanical failures happen (i.e. not caused by a sharp object piercing the tube).

Three options here,
Butyl tubes not Latex.
Tube size a little smallish for the tyre.
Valve not true through the rim, offset just a little.

__________________
Cheers,
George.

Make sure when you fill up the tyre not to yank too hard on the air hose connector. Do you have those little locking rings on the valve stems? If not, try holding the bike wheel and using both thumbs to remove the air hose connector with slow, steady force.

Another slightly possible cause is bad rim tape is cutting the rubber.

I think it's an incorrect alignment of the stem with the hole in the rim.

Good luck. report back when the problem is solved.