A vehicle tire deformation device for determining the size of a deformed contact patch of a tire which contacts the ground, said device comprising a movement detector connected to an attachment body by means of a moveable indicator element wherein both the movement detector and the attachment body are attachable to an inside surface of the tire, and wherein the size of the deformed contact patch of the tire is determined by the detector sensing a change in angle of the moveable indicator element indicating the border between the deformed contact patch of the tire and a non deformed part of the tire which is not in contact with the ground.