A Variable Ratio Gearbox (VRG) can be used in the drivetrain of a small to medium-size wind turbine to improve aerodynamic efficiency. Currently, all commercially-available wind turbines operate using a fixed-gear ratio between the turbine rotor and electrical generator. A VRG allows wind turbines, with a constant-speed generator, to discretely vary rotor speed and to achieve greater aerodynamic efficiency. The authors' previous results demonstrate the viability of the VRG design. This research quantifies the gain in efficiency for a VRG-enabled wind turbine based on wind data from representing all seven wind classifications. A method is also presented to identify turbine sites that provide the VRG with the greatest opportunities to increase production. The overall findings suggest that the VRG can benefit all wind turbines, irrespective of wind class, with some wind profiles in the study experiencing gains greater than 10%. (C) 2012 Elsevier Ltd. All rights reserved.