# Optimal Design of an Ecofriendly Pickup Truck Overhang and Roof to Reduce the Drag Coefficient
## 6 Conclusions  
In this study, a numerical analysis was conducted on the influence of the roof conditions and overhang length of a pickup truck on the drag coefficient, which has not yet been researched. Six factors (\(L_{T},L_{O},L_{C},L_{F},\theta_{F},\text{ and }\theta_{R}\)) were used in this study, and the flow was analyzed after creating 54 pickup truck models by combining the factors. Accurate flow analysis of each condition was performed by varying one factor while maintaining the others constant. Four geometric conditions (front angle, rear angle, angle position, and overhang length) were analyzed using the flow field and velocity profile.  
An increase in the front angle results in the rearward movement of the flow separation point, leading to a reduction in the wake zone size and consequently lowering the vehicle's drag. Moreover, a larger front angle facilitates a seamless integration between the windshield and the roof, diminishing the flow resistance arising from geometric factors.  
Similarly, an increase in the rear angle directs fluid toward the tailgate, thereby reducing the size of the upper wake zone and promoting more stable fluid flow. When the angular position is situated towards the front section of the roof, the momentum increase induced by the velocity exerts a more significant impact on the drag than the separation point position does. Furthermore, an elongated front overhang encourages a smoother fluid flow toward the windshield along the sufficiently extended bonnet. Consequently, a smaller wake zone forms at the junction between the bonnet and the windshield, resulting in a reduced drag coefficient.  
The lift coefficient showed the same tendency as the drag coefficient under changes in the rear and front angles. The lift coefficient significantly decreased as the overhang length decreased. The energy reduction rate exhibited the same tendency as that of the drag coefficient. Therefore, the energy consumption can be reduced by increasing the rear angle, and the driving resistance can be minimized by decreasing the overhang length. Therefore, the more the front and rear angles are increased, the closer the angular position of the roof is to the windshield, and the longer the overhang length is, the more optimal the design is to reduce the drag coefficient when designing a vehicle.  
This study investigated the front overhang and roof design of pickup trucks, which had rarely been done before. Based on the results of this study, we analyzed the trends in the drag coefficient, lift coefficient, and energy reduction rate for a total of 54 shapes, derived the drag coefficient correlation equation, and verified the validity of the correlation using an additional model. Recently, as the demand for electric vehicles has increased, the number of automobile companies releasing electric pickup trucks has increased. Through the correlation equation of the derived shape factors, it is possible to derive an optimal design that can reduce drag, which has a significant impact on the driving distance of electric pickup trucks.  
Conceptualization, T.K.K. and M.S.K.; methodology, T.K.K. and Y.B.; software, J.K. and Y.B.; validation, T.K.K. and M.S.K.; data curation, M.S.K. and Y.B.; writing--original draft preparation, M.S.K.; writing--review and editing, T.K.K. and J.K.; visualization, M.S.K.; supervision, T.K.K. and M.S.K.; project administration, T.K.K. All authors have read and agreed to the published version of the manuscript.  
Korea Institute for Advancement of Technology (KIAT): P0008458.  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
This research paper was supported by the Education and Research Promotion Program of KOREATECH in 2022.  
The authors declare no conflicts of interest.