The Indy 500 was actually part of the official Formula 1 calendar from 1950 to 1960, though the two series diverged after that.
Some Indy features (refueling, changing tires even if they didn't have a puncture, safety cars) got adopted by F1 through the 1980s, specially as F1 started to lose audience to the American series in the early 1990s.
Some Indy features (refueling, changing tires even if they didn't have a puncture, safety cars) got adopted by F1 through the 1980s, specially as F1 started to lose audience to the American series in the early 1990s.