Continuity mistake: In the early part when Peter Fonda and Dennis Hopper are getting their choppers ready, the film clip was reversed. You can tell because the American flag on Fonda's jacket has the stars on the right shoulder, not the left like the rest of the movie. (00:06:10)
Continuity mistake: At the beginning of the redneck cafe scene, George is seen entering wearing his helmet and he can be seen in a mirror to be sitting. When the camera switches to the guys' table, continuing the motion, George's helmet is sitting on the table. (01:04:47)
Continuity mistake: Billy and Wyatt and the two commune women are having a swim in a water basin. Wyatt is sitting on the rim, splashing his feet in the water, and 'his' girl starts swimming towards him. Then it cuts to a frontal close-up of her smiling at him, but you can still see his feet splashing in the background. (00:39:30)
Continuity mistake: In the film's final scene, the pick-up truck is never visible on the road except when it is being shown in close-up; for instance, as the camera pulls back after Wyatt's bike explodes, it should be driving up the road but is nowhere in sight.
Continuity mistake: After Billy gets shot and Wyatt rides towards the pick-up it's sunny with trees casting shadows on the road when the camera shows the pick-up, but not when it shows Wyatt. (01:29:35)
Continuity mistake: When everyone is sitting down eating at the rancher's house, just as he's saying grace, the rancher takes his false teeth out and puts them in his pocket. In the very next scene they are back in and he's chewing again. (00:14:45)
Continuity mistake: In the LSD scene in the graveyard there are a few shots of Wyatt where the eye injury he received in the red-neck beating isn't there (like when he holds on to the statue and says 'I hate you so much'). (01:21:45)
Continuity mistake: When Peter Fonda takes his watch off his wrist to throw it to the ground. When it is on his wrist it is a very expensive Rolex - when it hits the ground it is a cheap Timex.
Answer: Hopper is riding something British, Triumph or BSA. Hard to tell them apart and both were real common at the time.