Drag reducing apparatus for the rear end of a road vehicle such as a truck or trailer comprises a storage container in which an inflatable bladder is rolled on a support shaft for displacement relative to the container between a stored position and a deployed position in which the inflatable bladder covers the rear surface of the vehicle and is inflatable to provide an aerodynamic contour extending rearwardly of the vehicle. The inflatable bladder is extendable and retractable relative to the container by cables having ends attached to the container shaft and opposite ends connected to a cable shaft, whereby rotation of the latter pulls the inflatable bladder from the container and rotation of the container shaft in the opposite direction rewinds the bladder into the container for storage. Guide and support tracks and a spring clip arrangement hold the periphery of the bladder against the rear surface of the vehicle when the bladder is in its deployed position.