A crossbar clamp actuator of a crossbar-to-vehicle coupler may include a horizontally traveling wedge block having a ramped, downward-facing first slide surface, and a wedge follower having a second slide surface in frictional contact with the first slide surface of the traveling wedge block. Substantially horizontal repositioning of the traveling wedge block may cause the ramped first slide surface to urge the wedge follower downward, thereby actuating a crossbar clamp.