In a cost-cutting move, however, Ford Motor Company forced the Mark IV to increase parts commonality with the Ford Thunderbird; while the roofline, doors, and inner body panels were shared, the Mark IV and Thunderbird still were given different outer body panels below the roofline and different interiors. In a major break from American luxury car tradition, the rear wheel openings of the Mark IV were designed at the same height as the front wheels (similar to the 1966-1970 Oldsmobile Toronado); its large fender flares precluded the use of fender skirts.