The predecessor to the NASCAR Whelen Modified Tour was NASCAR's National Modified Championship, which was determined by total points from weekly NASCAR-sanctioned races as well as a schedule of national championship races. Parts of the northeastern and southeastern US were hotbeds of modified racing in the 1950s and 1960s; some racers competed five nights per week or more. Often the same car was raced on both dirt and paved tracks, changing only tires and perhaps springs and shock absorbers. In the late 1960s and early 1970s, the technology of dirt and pavement modifieds diverged to make them separate types of race car. NASCAR was no longer sanctioning dirt tracks which held modified races, so the NASCAR modified rules became the standard for asphalt Modifieds. (Starting in the early 1970s, northeastern US dirt modified racetracks began to join the DIRT organization founded by Glenn Donnelly.) Most unsanctioned tracks used similar modified rules to NASCAR's, or specified the same cars with cost-limiting rules such as smaller engines or narrow tires.