At the time of filming in 1966, cast members Mireille Machu and Jack Nicholson had just begun a serious relationship that continued through the making of Easy Rider (1969). In May of 1969, she accompanied Nicholson to the Cannes Film Festival as the latter was being screened. After they broke up, they remained friends and Machu occasionally would house-sit at Nicholson's Los Angeles home on Mulholland Drive during the 1970s.
The soundtrack includes a song called "A Study in Motion #1" sung by the Los Angeles band, The Poor. The group's lead singer and bass player was Randy Meisner, five years before he joined the Eagles.
It was a common practice for American-International Pictures to premiere their releases at drive-ins months before any theatrical release was made. This is demonstrated by an advertisement for the State Line Drive-In in Hagerstown, MD, in the movie section on page 30 of the Hagerstown Morning Herald, Thursday, February 16, 1967, in which the following appears: STARTS TOMORROW- PREMIER SHOWING, 2 TERRIFYING HITS WILDER THAN 'THE WILD ANGELS'. Call them punks...them animals.. you better get out of their way! 'Hell's Angels on Wheels'! They're souped-up for thrills and there's no limit to what they'll do. Behind the HEADLINES! Cycle Maniacs and Reckless Women.
Ralph "Sonny" Barger aka Sonny Barger was the Oakland President of the Hell's Angels, and is seen briefly at the beginning of the movie for which the Hell's receive collective credit. Barger plays and is featured in Hell's Angels '69 (1969).
Mentioned in the wedding ceremony, Darrell Whitman and Abigail McKinnon are Gypsy and Abigail's legal names, respectively.