The present invention relates to a device for the automatic demounting of a tire from a rim having: - a support arm being liftable and lowerable in a direction substantially parallel to the rotation axis (x-x), - a demounting tool articulated to the support arm, - an attachment member for the demounting tool, comprising a first and a second articulation pin extending substantially parallel to each other, - at least one extension appendage of the support arm or a section of the support arm, which extends beyond the second articulation pin, and - at least one tie rod member that is articulated on one side to the tool, and on the other side to the extension appendage or section of the support arm.