>>1686725a bicycle rim looks like this right
that lip at the top is called the hook
the bead of your tire seats against that
the well in the middle of the rim has a smaller circumference than the lip
Make sense?
so when you're trying to push a bit of tire bead on/off the rim, going all the way around the tire, pushing the rest of the tire bead into the well, will create slack. Just keep doing that on tough tires each time you move a bit more on/off.
