Is anyone aware of any SYSTEMATIC studies of tire tubes? I just can't figure this one out. I've had all kinds of tubes fail on me. The most common problem has been the valve seat. (I think some people call that the valve boot.) It happened with two Bontrager tubes but I've had it happen with other brands, too. I think that I may have caused some of the failures by tightening the valve locknut too tight up against the rim, but I've seen at least one more valve seat failure since then. I'm wondering whether it's better to not use that locknut at all. The Michelin tubes don't even have a threaded valve stem, so it doesn't appear to be necessary.