This is a problem that I have been troubled with for some time now. I have asked many people but have yet to find a solution. I run Geax Sedonna tires on disc Sun rims on a XC bike. My front tube is regullary destroyed when the vavle stem breaks at the base. I have tried many things to alleviate this problem.

Filed and smothed the valve hole
Used a peice/s of rubber to cushion athe vavle stem at the hole
Increased tire pressure
Changed tube brands

I am at wits end! Please help me solve this.

Thanks

If I were you i'd try a couple more things before going insane.
Id try gluing the bead of one side of the tire to the rim incase maybe the tire is rotationg and taking the tube with it. I used to do this in dead of winter running really really low pressures.
Or try maybe using a presta valve with one of those valve adaptors.... might help cushion the vavle... Other than that.. i got no clue

luke.harrison has got it 100%. This is cuased by the tire creeping around the rim under hard braking and pulling the tube with it. You may also try putting talcum powder on the tube so it doesnt stick to the tire. I have seen this more often with under inflated rear tires under the driving load.

You know the retaining nut that keeps the Presta valve in place against the rim? You can use two of those: one on the outside (normal place) and a second on the inside.

When installing a new tube, install a retaining nut on the valve *first*, then put the valve through the hole, put the second retaining nut on the valve, snug it to the rim, finish installing & pump tire as usual.

Good luck!