When replacing a rotor, make sure to tighten or secure it according to the manufacturer's recommendations.
On some vehicles the rotors are directional. These ventilated discs have curved cooling fins.
Some ventilated rotors have curved cooling fins and are directional. Courtesy of EIS - Standard Motor Products.
For maximum cooling, these fins must point rearward at the top of the rotor. This allows centrifugal force to spin air outward from inside the rotor.