Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel, because on heating the iron rim

The iron rim is generally made slightly smaller than the wooden wheel. When heated, the metal expands, and increases in size, being able to fit on the wheel. As the metal cools down, it comes back to its original state and regains it’s size, fitting tightly onto the wooden wheel.

This is an example of physical, reversible change.