This was originally to have been a low-budget, made-for-TV movie. However, Paul Newman, who had just caught the "racing bug", heard about it, decided it was the kind of movie he wanted to do, and it was soon elevated to a big-budget "A"-list feature film.
The crash sequence at the beginning of the Indianapolis 500 was from the 1966 race. In this sequence, A.J. Foyt can be seen climbing over the first turn fence to escape the crash site.
Paul's brother, Arthur Newman appeared in this movie as a stand in for Paul during some of the more dangerous scenes. You can see him if you stop the movie and go frame by frame and look very carefully, as they do resemble each other quite a bit.
Additional footage needed after the 1968 Indy 500 was filmed at Indianapolis Raceway Park.
The winning car of Frank Capua (Paul Newman) is painted to resemble the #3 Rislone Special driven to victory in the 1968 Indy 500 by Bobby Unser. Unser makes a cameo appearance, congratulating Capua on his victory.