An air dam assembly mounted under a front end of a vehicle includes a passively deployable air dam assembly. The passively deployable air dam assembly includes a passively deployable air dam having a front surface at least partially exposed to ram air when the vehicle is traveling in a forward direction, and a passive deployment assembly including at least one spring biasing the passively deployable air dam into a retracted position, with the passive deployment assembly engaging the passively deployable air dam to allow the passively deployable air dam to move, against the bias of the spring, from the retracted position to a deployed position closer to ground under the vehicle when a forward speed of the vehicle reaches or exceeds a predetermined activation speed.