During a decade spanning the 1970s and 1980s, Dryden researchers conducted tests to determine the extent to which adjustments in the shape of trucks reduced aerodynamic drag and improved efficiency. During the tests, the vehicle's sides were fitted with tufts, or strings, that showed air flow. The investigators concluded that rounding the vertical corners front and rear reduced drag by 40 percent, yet decreased the vehicle's internal volume by only 1.3 percent. Rounding both the vertical and horizontal corners cut drag by 54 percent, resulting in a three percent loss of internal volume. A second group of tests added a faired underbody and a boat tail, the latter feature resulting in drag reduction of about 15 percent.
