The R1 Concepts Geo-Carbon drilled-and-slotted rotor is listed as a rear left replacement for 1978–1983 Dodge Challenger models. The description specifies a Geo-Carbon rotor with drilled and slotted features for the rear left position; use it as the axle- and side-specific replacement and obtain the complementary rear right rotor if replacing both rear rotors.
R1 78-83 Dodge Challenger Rear Left Drilled & Slotted Geo-Carbon Rotor