— Narrow Tilting Vehicles (NTVs) are the convergence of a car and a motorcycle. They are expected to be the new generation of city cars considering their practical dimensions and lower energy consumption. But considering their height to breadth ratio, in order to maintain lateral stability, NTVs should tilt when cornering. Unlike the motorcycle's case, where the driver tilts the vehicle himself, the tilting of an NTV should be automatic. Two tilting systems are available; Direct and Steering Tilt Control, the combined action of these two systems being certainly the key to improve considerably NTVs dynamic performances. Focusing on the lateral dynamic of NTVs, multivariable control strategies based on linear robust control theory, were already proposed in the literature, assuming decoupling with the longitudinal dynamic. In this paper a 4 DoF model of the main longitudinal and lateral dynamics is considered, and its differential flatness is demonstrated. The three flat outputs have furthermore a particular physical meaning, making possible the design of a simple external control loop complying with the driver demands.