Abstract: In modern automotive wind tunnels, wheel spin units (WSU) are used to simulate rotating wheels, but their finite-sized moving belts inevitably disturb the local flow, creating induced drag and resulting in measurement error. This study experimentally investigates the pressure field disturbance caused by the ground opening and moving belt of an isolated WSU in the aeroacoustic wind tunnel at the Shanghai Automotive Wind Tunnel Center. The experimental data are verified using steady Reynolds-averaged Navier-Stokes (RANS) simulations. Results show that the primary source of induced drag error is the pressure difference between the leading and trailing edges of the moving belt. Installing a flow control device is shown to attenuate the flow disturbance, reducing the induced drag error by approximately 30%. Numerical simulations confirm the effectiveness of this measure, predicting a drag reduction of 30.9%. This work demonstrates that such a device can mitigate WSU-induced flow field perturbations and improve the accuracy of aerodynamic drag measurements in wind tunnel testing.