An agricultural tool includes a wheel body and a flexible tyre with a hollow chamber and an inner surface around this hollow chamber; a circular opening on the chamber; a pair of beads bordering this opening; and a spacer at least partially tubular with two axially opposite end faces. Over one portion corresponding to one of the beads, the inner surface extends frustoconically by widening radially outward of the flexible tyre, and one of the end faces of the spacer has an axially protruding surface. The spacer is placed across the opening of the tyre such that the protruding surface engages the inner surface in an area of the portion corresponding to the bead.