An Updated Correlation Study between the Full Size Wind Tunnels of General Motors, Ford Motor Company, and FCA US LLC

As automotive aerodynamic testing facilities evolve to capture more real-world behavior, updating the correlation between old and new technologies is essential. Recently, the three-member consortium of the United States Council for Automotive Research (USCAR) - FCA US LLC, Ford Motor Company, and General Motors - transitioned from full-size static ground plane facilities to 5-belt moving ground plane wind tunnel facilities. The primary objective of this study was to update the correlation data sets to maintain consistent and robust data sharing among companies, which is the cornerstone of USCAR efforts. To achieve this, a set of updated correlation data sets were calculated to replace the original correlation study results from 2008. Additionally, the methodology for applying correlation equations was revised from using averaged wind tunnel data to employing direct wind tunnel-to-wind tunnel correlation equations. In a two-phase correlation effort conducted in 2022 and 2025, the three companies exchanged and evaluated six vehicles of varying size and proportions across the three rolling road wind tunnels. To ensure the updated correlation data sets capture the bounds of current and future vehicle aerodynamic performance, the tested bandwidth of coefficient of drag area (CDA) data ranged from 0.37 m2 to 1.45 m2 (CD from 0.17 to 0.48). Despite the unique challenges of each wind tunnel project, the outcome of the updated correlation efforts demonstrated excellent correlation (R2 > 99.9%) across direct tunnel-to-tunnel comparisons, mirroring the success of the original 2008 correlation efforts. These findings validate the accuracy and reliability of aerodynamic data collection in each of the three rolling road facilities, thereby supporting consistent and robust data sharing among USCAR partners.