This paper discusses the influence of the buckets overlap ratio of a Savonius wind rotor on the averaged moment and power coefficients, over complete cycles of operation. The continuity and Reynolds Averaged Navier-Stokes (RANS) equations, and the Eddy Viscosity Model k-omega, SST, on its Low-Reynolds approaches, using hybrid near wall treatment; are numerically solved by the commercial software Star-CCM(+). This software is based on Finite Volume Method and computes the pressure and velocity fields of the flow and the forces acting on the rotor buckets. The moment and power coefficients are achieved by integrating the forces coming from the effects of pressure and viscosity of the wind on the device. The influence of the buckets overlap ratio on the moment and power coefficients is checked by changing the geometry of the rotor, keeping the Reynolds number, based on rotor diameter, equal to 433,500. The results obtained for the rotor with zero overlap are in agreement with those obtained experimentally by other authors what indicates that the method can be successfully used for such analysis. The values of the moment and power coefficients obtained as a function of tip speed ratio and the buckets overlap of the rotor indicates that the maximum device performance occurs for buckets overlap ratios with values close to 0.15. (C) 2011 Elsevier Ltd. All rights reserved.