Problem. The tendency to reduce the working volume of internal combustion engines, which has emerged in recent years in the global automotive industry, is due to the need to improve the environmental situation and energy efficiency of road transport. Goal. The aim of the study is to increase the energy efficiency of vehicles by rationally reducing the maximum effective engine capacity. Methodology. The work uses the method of partial accelerations, implemented in a mobile registration and measurement complex, which allowed the authors to obtain an improved formula for calculating the force of aerodynamic resistance. Experimental studies of car aerodynamics were also carried out. Results. The article presents the results of the authors' research, which made it possible to prove the possibility of reducing the power of the internal combustion engine while maintaining the specified maximum speed and the specified level of indicators of the dynamic properties of cars. Originality. The relationship between the degree of use of the maximum engine power and the relative change in the effective specific fuel consumption of a carburetor gasoline engine with direct injection of gasoline and diesel is determined. Practical value. Calculations performed on the example of the ZAZ-1103 "Slavuta" car showed that a rational reduction in effective power allows for a 9.5% reduction in fuel consumption, and for an engine with direct injection of gasoline and diesel engines, this leads to an increase in fuel consumption by 6.7 % and 20.3%, respectively.