Why does the iron tire, which is put on the wheel rim of the cart, the blacksmith heats up strongly before putting it on?

Iron, like many other materials, expands when heated.
The iron tape, closed in a ring, which forms the tire of the wheel, increases its size with strong heating, including adding a little in diameter.
This allows the smith to fit the tire precisely onto the rim.
When it cools down, the size of the tire-tape decreases (including its diameter), and it tightly wraps around the wooden wheel rim.
This arrangement ensures further reliable service of the iron bus.