It is The Lost Traveller (1977) by Steve Wilson.
The main character in the novel is called "Long Range" or something similar.
Long Range's mind raced; then as he entered the pass, he wheeled his machine about, stopping for a moment to wipe his hand across his dusty face and red-rimmed eyes. He jerked the shotgun from his saddlebag and, holding it in his left hand, nosed his bike back down the narrow trail. As he approached the bend he could hear the sound of motors laboring up the mountain toward him. He cocked the shotgun with his thumb, feeling completely cold but fiercely elated.
It's about biker gangs roaming post-apocalypse USA
In the dark world after the nuclear apocalypse, a nascent civilization turns to the Hell's Angels to save the scientist who can reclaim the Dead Lands...
Also involves some Native American tribes and rituals.
The Hell's Angels were in conflict with their biker rivals, the Gypsie Jokers. I was going to point out that it was not a bad book, but just that it did not read quite like science fiction. Then about halfway through the book the Hell's Angels protagonists encounter and join up with Lakota Indians who, in this post apocalyptic world have gone back to the "old" ways. Then it starts to read like an historical western. The Hell's Angels even give up their motorcycles for a time to ride horses. At that point, though, the fragmentation of North America starts to hit home.
Goodreads, Lost Traveller, Roger Bailey's review