Motorized seatbelt systems that retract seatbelts using motors are being mass-produced by many manufacturers. Scenarios for operation of these systems cover a wide range, including automatic braking for collision avoidance, brake assist and other such pre-crash situations, when the seatbelt is buckled, unbuckled and stored, during sport driving, or under normal conditions. These systems increase the retracting load of the motor using gears, and they can apply a high load in retracting the seatbelt. Previous systems, however, were designed primarily for pre-crash conditions. In previous systems, motor speed rose to higher levels in the normal operating state. The tendency to generate more noise and the application of higher loads on seatbelt retraction therefore became issues. For the present study, these issues were addressed using simulation to optimize the gear ratio. Using this method, the present system successfully reduced the noise during operation by 12%, reduced the load during normal usable operation by 36%, reduced the chest load during pre-crash situation by 20% and provided occupant protection performance on a par with previous systems.