I have had that problem,especially with new sand tires. first always have the valve core out for maximum air. With a DRY tire and wheel try to push the bead on as far and tight as possible on the tapered side of the wheel.(the side you don't mount on) with your chuck on the valve stem, your knee in the middle on the wheel, and with both hands,and maybe even a buddiies, pull the tire very gently over to the other side. When your tired of "that was close but the back popped off" try it with a blow gun or two at the bead,( not one of those sissy safety low pressure blow guns) the more air in the better. If all fails or your compressor doesn't have that much reserve, then a LITTLE bit starting fluid or brakeleen and throw a match. (Probably should not be telling people to do that-legally) Or find a tire shop with a Cheetah (I made one out of an old air bubble-cuz dam they're expensive)