This wasn’t an bikie gang in the sense of the Hell’s Angels or Bandidos (who probably tend to be on the conservative side). This was multiple bike-stunter clubs riding around NYC raising a ruckus, and pissed off because the cops wouldn’t let them into Times Square.
Come to think of it, this was probably what the gangs were like in the 50s and early 60s, before they got older, organized, and into real crime rather than petty crap.