Cost benefit and teraflops restrictions imposed by the sanctioning body made steady-state RANS CFD simulation still a widely accepted first approximation tool for aerodynamics evaluations in motorsports, in spite of its limitations. Researches involving generic and simplified vehicle bodies have shown that the veracity aerodynamic CFD predictions strongly depends on the turbulence model being used. Also the ability of a turbulence model to accurately predict the aerodynamic characteristics can be vehicle shape dependent as well. Modifications to the turbulence model coefficients in some turbulence models have the potential to improve the predictive capability for a particular vehicle shape. This paper presents a systematic study of turbulence modelling effects on the prediction of aerodynamic characteristics of a NASCAR Gen-6 Cup racecar. Steady-state RANS simulations are completed using a commercial CFD package, STAR-CCM+, from CD-Adapco. Five turbulence models are included in this study: the standard, realizable, AKN low-Re variants of the k-ε model, and the standard and SST versions of the k-ω model. Selected closure coefficients, such as σ_k, σ_ε for the k-ε model, and a_1 for the SST k-ω model are slightly modified in order to investigate the sensitivity of these closure coefficients on the veracity of predictions. The aerodynamic characteristics investigated include the force and moment coefficients, and front-to-rear downforce balance. In addition, the turbulence mode dependence of the flow around the vehicle, particularly at some key locations will be analyzed. Although, the flow features in the wake of this racecar show a discernable dependence on the choice of the turbulence model, this difference did not translate into a significant difference in the prediction of force coefficient.