i dont even use tire irons (AKA tire levers). Push the stem in a bit, then squeeze the tire at the stem so the beads go into the channel at the center of the rim. Then grab both sides of the tire, pulling as you move your hands away and to the oposite side from the stem. With practice you will have enough "slack" to easily pull the tire over the rim at the opposite side from the stem. Using that approach, I popped off my rear last night for a flat fix in about 10 seconds.
Every time you use irons, you risk damaging a tube. Learn to do it with out - much better.