Voyage to the Planet of the Bikers is the first half of episode 12 of season 3 of My Life as a Teenage Robot.
Tuck is riding his tricycle and some kids are picking on him. He decides to learn how to ride a two-wheeler, but fails. Meanwhile, Jenny is fighting the Space Bikers. It ends as her getting turned into a bike, and they made it so she can't change back. She tells Tuck that he needs to get on her to work the throttle, but he says that he needs training wheels on her first, so he puts them on her.
After Jenny and Tuck chase the Space Bikers for a while, the bikers blast off into space. Jenny says that they are going to the planet of the bikers, and Tuck has a scary little abstract nightmare, as the planet of the bikers are full of bikers, for a while. When Jenny goes to pick out a space ship to follow the bikers, she initially picks a really high tech battleship, but Tuck deems it too scary and makes her take a ladybug ship for old ladies that Ms. Wakeman takes for picnics on the Moon.
So they go to the Space Bikers' planet but quickly realize that the planet is full of nice people and pastel colors. They find the bikers and see that they are school administrators. They think that this is a disguise, but then are told that they are really school administrators. But when they get evidence that the bikers are bikers, and the bikers, fearing that their secret will be blown, stupidly get into costume and chase them around, with everyone seeing.
In the end, the bikers' normal lives are utterly ruined, and to prevent evidence of them being all cheery and pastel from getting to their evil friends, they turn Jenny back to normal, and Tuck realizes that since the training wheels fell off during the chase, he can now rub it in the bullies smug faces. And he does.