RTRI Large-Scale Low-Noise Wind Tunnel uses wire balances to measure aerodynamic forces of a wire-supported train model on a moving belt ground plane which simulates the flow between the ground and the train model under the actual condition. Measurements of aerodynamic forces, especially those of aerodynamic drags, require correction of tare drags exerted on wires. This paper reports the usage of the wire balance, its accuracy, method to correct the tare drag and comparison with the results of wind tunnel test on the same model in German-Dutch Wind Tunnel (DNW).