Originally Posted by
catgita
Nope, I don't buy it. I have had several tubes develop leaks around the valve stem, either directly at the stem (not in many decades), or around the boot. There definitely was not any unusual stress on the stem. If it can't take the usual stresses (like with a dead straight and free to move stem), that is a defect. Recently had a Shwalbe ($$$) tube show a string of bubbles around the stem boot in a dunk test.
I quit using cheap tubes because the valve plungers would snap in two (and purchased a mini pump with a hose). A problem I never had in 150k miles, but then had 4 times in one month, while using pumps I had used for years. Probably a bad batch, but still.
Frankly, I would not take the word of a bike shop that tubes are NEVER defective. It is called denial. Sh.. happens, test your spare, and toss the bad ones.
BTW. Why would tube prices be going up significantly?
I agree with your ---(like with a dead straight and free to move stem)--- line. It is just so very rare when a tube is truly defective. How come when installed by the bike shop tubes don't have the "defective" issue? I am certain that once in a blue moon you will find a defective tube but as I stated earlier---both Kenda and Duro pretest all tubes under pressure.