In 1982 a test was conducted by Popular Mechanics without any variables attempt the aerodynamics of a truck and whether taking simple measures to improve the aerodynamics in the place of truck affected the fuel economy or don't. They had put on a tonneau cover on an open bed truck and drove it to have distance. Certainly they drove identical shoes you wear truck with tonneau hide. The mileage increased by a staggering 9% at a time cover. The drag involved with the open bed on the truck when your experiment showed was eliminated by the tonneau cover. Popular Mechanics further insisted on installing a camper shell. A camper shell, they said, would cover any turbulence at the rear of the vehicle created using the cover as well as the air caught in the space and would eventually boost mileage by 13%.