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The importance of energy efficiency, as one of the most crucial issues in automotive industry, has grown more rapidly considering the global energy crisis and climate change in recent years. This paper aims to introduce a method to increase the powertrain efficiency based on the minimization of tire power loss. Slip resistance is taken into account as well as rolling resistance to yield the modified tire resistance considered in this study. It is shown that the general optimal control problem can be reduced to an instantaneous minimization problem in which the equivalent force of tire power loss is to be minimized at each instant of time. Moreover, tire inflation pressure is selected as the control input bearing its major influence on tire resistance and its potential of being controllable in the mind. In addition, a polynomial inverse tire model is developed in order to find the solution of the minimization problem with lower computational cost. The coefficients used in inverse tire model are characterized as a function of friction coefficient, normal load, and inflation pressure so that the reliability and accuracy of the model are guaranteed under different conditions. The effectiveness of the proposed online control system, called Tire Inflation Pressure Regulation System, is simulated in some driving cycles, i.e. NEDC, FTP, HWFET, and ARTEMIS-Urban, and it is shown that up to 2% improvement is achievable.