 If there are 40 or less (or 32 or less) vehicles entered in the respective races, no provisionals are charged and the field will be determined by timed laps only.After these positions are awarded, the cars are arranged by lap times.In 1991, NASCAR introduced the past champion's provisional (sometimes known as the "Petty rule") after Richard Petty failed to qualify in four races in 1989, which resulted in a viewership ratings drop that season.