The paper presents both the exact and simplified relations on the course of the reaction torque of a single and multi-cylinder engine, which is transmitted to the vehicle frame or foundation. The formula for the distance between the balance shafts along the vertical axes ensuring a complete elimination of the impact of the forces of inertia on the course of the reaction torque in four-stroke four-cylinder engines is derived in the paper. The criteria for selecting the optimum value of the distance are also derived in the paper. The dependence of the optimum value of the distance on the state of the engine operation and design parameters of the vehicle propulsion system is indicated in the paper. The paper proposes the selection of the optimum shafts distance, for a given type of vehicle, in areas of the engine most frequently used operating states.