I had that problem before, what happened is when the tire dropped to the central ridge the tape, as it's not very flexible, lifted from the sides. As you pump the tire it will move to the rim walls, pushing the tape back into place. If the tape is too small it may not get trapped between tire and rim, and air could slid under making the whole operation fail.
I had that problem before, what happened is when the tire dropped to the central ridge the tape, as it's not very flexible, lifted from the sides. As you pump the tire it will move to the rim walls, pushing the tape back into place. If the tape is too small it may not get trapped between tire and rim, and air could slid under making the whole operation fail.