Abstract: An air drag reducing apparatus is mounted on the rearward surface of a large vehicle. The apparatus comprises first and second pairs of identical panels having a base edge and first and second side edges extending from the base edge, and mating hinge plates and hinge pin. The base edges of the first pair of panels are adapted for mounting to one of the opposed vertical side edges of the rearward surface of the large vehicle and the base edges of the second pair of panels are adapted for mounting to one of the upper and lower side edges of the rearward surface. The second side edge of each of the first pair of panels is hingedly connected to the first side edge of a respective one the second pair of panels so as to form one of two fold-away portions of the apparatus. Each of the panels is symmetric about a respective axis of symmetry. At least one of the angles formed between the edges of the panels and the sides of the rearward surface of the vehicle is between 18 and 30 degrees.