An inlet, positioned to access the flow of air passing around and under a moving vehicle, draws in air which is conveyed through a duct and discharged to cool a brake on a vehicle. The inlet has a closure so that access of cooling air may be denied when the brake temperature is less than a predetermined temperature and opened only when the brake temperature exceeds that predetermined temperature. The closure is operated by a temperature-operated actuator. In embodiments the actuator may be suitably positioned to sense a temperature representative of the brake temperature and to incorporate a thermally activated phase change, active or smart material preselected to operate the inlet closure when the sensed brake temperature exceeds the predetermined temperature.