Just changed to the Shinko 241 tires and used tire talc in the process and am now wondering if that was a mistake. On the second ride the rear valve stem ripped out of the tube and am wondering if that may have been because of using tire talc. One thing about it is that the problem was caused by something I did wrong. The other possibility is that I messed up in tightening the nuts on the valve stem. The tire talc is some slippery stuff but was careful not to get any on the tire bead. Any advice from more seasoned members than I would be appreciated.