A drag reducer adapted to be mounted on the rear face of a land vehicle. It is characterized by a large piece of flexible material adapted to be tightly fixed around the periphery of the rear surface adjacent the lateral faces of the truck. The piece of material has an area larger than the rear face of the truck so as to display a convex surface when fully extended. The drag reducer has one and preferably two openings located adjacent the periphery of the rear face of the truck and a tubular extends from each of the said opening in a direction towards the front of the truck so that upon forward movement of the truck, air is automatically introduced in said tubular members and projected between the rear face of the truck and automatically forming a plano-convex air bag which reduces the drag behind the truck.
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