Motorbike Parts are used to unlock the Biker Stewie and American Johnny, and can be obtained in the following ways:

- Making Jerome Sling Beers at the Biker Bar

- Making Peter Arm Wrestle a Biker

- Making Senpai Peter Bat His Eyelashes

- Making Undead Racer Bertram Practice His Evil Laugh

- Clearing Motorcycle Mutant