(The Strictly Stock Division, which evolved into today's premier Cup Series, did not race until 1949.) Post-World War II modifieds were a form of "stock car" (contrasted against purpose-built AAA championship cars, sprints, and midgets) which allowed some modification, typically substitution of stronger truck parts. Most cars were pre-WWII coupes and coaches. This pattern continued through the 1960s, with aftermarket performance parts and later-model chassis (such as the 1955–57 Chevrolet's frame) becoming more common. Modifieds became known for technical innovation, both in homebuilt parts and in adapting components from other types of vehicles. By 1970, many modifieds featured big-block engines, fuel injection, eighteen-inch-wide rear tires, radically offset engine locations, and other technologies that made them faster on short tracks than any full-bodied race cars including Grand National cars.