Road vehicle platoons improve fuel economy by limiting the aerodynamic drag. Time-headway along with op-erating speed dictates the intervehicular spacing, and hence the aerodynamic drag reduction. This paper proposes an adaptive scheme to adjust the magnitude of time-headway to reduce energy consumption according to operating speed. An ‘energy consumption - time-headway - speed map’ is generated using a complete vehicle dynamics-based platoon framework integrated with a sliding mode controller. This map could be used to adaptively adjust time-headway for an expected energy consumption magnitude and to predict the energy consumed for the completion of a route. Constraints are enforced limiting the time-headway values to meet deceleration demand. The proposed approach was found to result in an energy consumption reduction up to 35% compared to conventional approaches where the time-headway values are kept constant.