Originally Posted by
banerjek
One thing you can do to avoid this sort of problem is to partially inflate the tire (maybe to 20 lbs), then work the tire with your hands to make sure everything is seated and distributed properly, then inflate the rest of the way.
That helps for pinches elsewhere; but for the valve stem problem working the bead, it often doesn't help. What works is to push the valve all the way into the rim until it 'bottoms out' against the far side of the tire! If there's a little pressure in the tube while you do it, the tire will pop right into place with no further fiddling.
BTW, getting the tube stuck under the tire bead is not the source of 'pinch flats.' Pinch flats are caused by bottoming out the tire against the rim on a bump, and are characterized by two small holes ('snake bites') matching up with the rim edge that took the blow.