Originally Posted by
Al1943
Tubes torn at the base of the valve stem can be due to a problem with the rim, like a sharp edge. Or from having the stem rock back and forth from using a frame pump. Another possibility is a tube made defective during the process of molding the stem with the tube.
IMO tube thickness has little if anything to do with tube failure. In fact I've always had better luck with ultra light thin tubes, maybe because the quality control is better.
Al
Add to that list the tendency of a tire to slip and rotate on the rim, putting excess pressure on the valve stem. The tendency increases with heat and hard braking as the tire becomes more flexible.