Originally Posted by
Avalanche325
Here is the reason I do it:
Under hard braking, especially on fast descents, the tire slips on the rim just a tiny tiny bit. Without talc, the tube sticks to the tire and moves with it. As the tube moves, and the stem can't, it can rip the stem out of the tube. As most of the braking force in on the front, this where you are likely to have a blowout. Right where you don't want it!
The talc lets the tire slip on the rim without taking the tube with it.
It happens on MTBs more often because of the lower pressure. I did have it happen to me at 35MPH on a MTB. I damned sure never want it to happen on the road.
I deny that the tire-tube interface ever slips on an inflated tire. You can see the imprint of the casing on a used tube - that wouldn't be there if there were any slippage.
The idea that the tire would rotate on the rim without taking the tube with it is nonsense - what force keeps the tube from rotating? If the tire slips on the rim then the tube comes with it, talc or not. I'm not saying you won't experience a valve-rippage blowout; I'm saying talc won't prevent it.
I put a little baby powder in a new tire or a new tube, and I put a little in with my spare tubes in the seat bag - it helps with mounting but that's all.