My bike's better than me!
Joined: Feb 2005
Posts: 2,337
Likes: 582
From: Northern Colorado
Bikes: Moots Vamoots, 'Dale T2000, DB Response Comp, '98 G. Fisher HKEK, '89 Panasonic DX-6000, '88 Fisher Montare XT, '83 Nishiki Int'l, '72 MB GR, '75 MB GJ, '77 MB LC, '85 Centurion Ironman, '82 Miyata 710
1) Burr at the valve stem hole in the rim. Get a round file and carefully file it down. You may not feel it, but it may be there nonetheless;
2) Using valve stem nuts? Throw them away. You don't need them. People overtighten them--especially after inflating the tire. Sure recipe for a tear;
3) Using a decent floor pump, or a hand (mini) pump? If you're using a mini-pump, chances are, the back-and-forth (rocking) motion as you stroke the plunger are tearing the tube at the valve stem reinforcement. Use a decent floor pump.
4) Using a particular brand of tubes?? Try another. Performance cheapies are a bit notorious for this problem. Try Michelins (or something else).
Good luck!