As tractors replaced horses and oxen in the 20th century mechanization age, the sights and sounds on the farms changed as dramatically as they did in the cities with the advent of the automobile. The new motorized inventions allowed more land to be cultivated in less time, resulting in increased production. New sorts of problems accompanied this novel technology, however. The thrifty farmer needed to learn new skills to be able to repair the engines, just as he had learned to mend earlier farm tools. The steel wheels with lugs destroyed paved surfaces, confining the tractor to dirt roads. Because it could not drive on steeper grades without tipping over, farmers had to abandon hillside fields.