In the 33rd running of the Indianapolis 500 in 1949, Wilbur Shaw, the President of the Speedway, actually did drive the pace car, as the movie announcer had noted.
Spring Byington loved the Indianapolis area so much that she chose to live there in the early 1950s and was a local TV star with her own show and specials with parts in many other shows on local TV stations.
The movie is set in the fictional town of Carrell, California. However, this name is taken from an actual race track, Carrell Speedway in Gardena, California, where some of the racing scenes were filmed. Carrell Speedway existed from 1940 to 1954 on land owned by Judge Frank R. Carrell and predates the more well-remembered Ascot Park which opened in 1957 several blocks to the south.
The portion of the film set in Indianapolis used footage shot at the actual 1949 Indy 500 time trials and race, and other footage at the track. Other than Mickey Rooney's character Billy Coy, driving car #6, most of the drivers and car numbers cited by the announcer in the movie were the actual entrants in that race. Car #6 was actually driven by Lee Wallard who completed only 55 laps of the race. As in the movie, the race was won by #7, Bill Holland, but he actually won by a huge margin and didn't relinquish the trophy to another driver.