The development of Intelligent Transportation System (ITS) technologies is an emerging topic in regards to Powered Two-Wheelers (PTW's). Major researches on automobiles are still focused on the area of active safety systems which aim to minimize the risks of accidents by controlling the stability of the vehicle in critical situations. The main issue in designing stability control systems for motorcycles lays in the different and complex driving dynamics in comparison to four-wheeled vehicles. Nowadays the most sophisticated system available for commercial powered two-wheelers is the anti-lock braking system (ABS). Undoubtedly it provides safety benefits, but it is not designed to operate during strong cornering in presence of high lateral accelerations. For the design of motorcycle's safety control systems the set-up of a proper vehicle's model is a major issue. Often the model is required to be as simple as possible and able to describe the most of the roll dynamic behaviour, but these two requirements are conflicting. The author's prior works proposed an analytical model with rear wheel traction able to examine a motorcycle during acceleration and braking in straight running or cornering condition. This model linearized around the vertical position considers the coupling of the dynamics and provides an adequate description of the friction forces, hence it proves effective in describing the dynamics of a vehicle in curve. In this paper, in order to obtain a better understanding of the vehicle dynamics in critical situations, simulation tests and comparisons between the behaviours of the linearized model and the same model with no roll linearization have been made considering the vehicle in highside fall.