A roof fairing is a commonly used add-on for trucks or tractor-trailers, where a significant difference in height exists between the cabin and the container. A roof fairing reduces the aerodynamic drag on the vehicle by directing the onward wind flow smoothly onto the container and thus reducing flow separation in front of the container. Since standard containers are available in two different heights and there are cases when vehicles ply without load i.e. without a container, it is necessary to adjust the height of the fairing accordingly to maintain an optimum aerodynamic configuration. While adjustable fairings have been in use in the commercial vehicle industry, these fairings are usually shaped as flat plates, often with open sides for ease of folding. A highly curved and bulbous fairing helps in reducing drag better, especially in presence of side winds, although it makes adjustability difficult. The current paper presents the benefits of installing an adjustable roof fairing on a truck. It has been observed that a well profiled roof fairing gives 4.03% reduction in coefficient of drag over a bent plate fairing and the adjustable roof fairing provides 6.35% improvement in fuel savings compared to fixed roof fairing for the truck with tall container.