RESISTANCE FORCES WHEN DRIVING A PASSENGER CAR

Abstract

The discrepancy between the calculated and experimental values ​​of vehicle drag force in the 30–160 km/h range is explained by the use of a constant exponent, α = 2, in the aerodynamic drag formula. Based on road tests, an average α(v) relationship was obtained, with a minimum α = 1.98 at around 120 km/h and a maximum α = 2.15 at around 33 km/h. Including a variable α reduces the discrepancy by a factor of 5–10, increasing the accuracy of modeling and fuel consumption calculations.

Factor analysis revealed that the main differences between the calculated and experimental forces are due to imperfections in the aerodynamic drag model, especially during the transition from laminar to turbulent flow. Other factors—vehicle vibrations, H/B ratio, final drive ratio, and tire profile—have a significantly lesser influence. Aerodynamics is the most important factor: the Cx and Cx·F indices have virtually equal influence.

The average α(v) relationship is similar for all vehicle categories, although significant variability remains within each group. The introduction of variable α significantly reduces the discrepancies between theory and experiment, enabling more accurate calculations and predictions of vehicle dynamics. This allows engineers to adjust computational models, take real-world aerodynamic effects into account during design, and assess the impact of speed on air resistance. This approach also provides a basis for optimizing body and chassis design aimed at reducing fuel consumption and improving vehicle efficiency in real-world driving conditions. Furthermore, the use of variable α helps identify critical speed ranges where air resistance has the greatest impact on vehicle dynamics and can serve as a starting point for further research into improving vehicle aerodynamics and energy efficiency.