Also, Esperanza is just so lonely and sad. She is begging for friends, to the point where she is jealous of her brothers for being closer in age. She is disappointed in what she has (the house on Mango street, her siblings, and her name), and her goal to to be more than that. In a way, I think Esperanza connects her life to the house on Mango Street. When she talks about her goals, her goals center on having a big house, unlike the one she had on Mango Street. She feels tied to her house maybe, and its neighborhood.
This may be a stretch, but the bicycle may represent her desire to move- to move out of her life. She traded Cathy (who is a total snob) to have part of the bicycle. Even though she, Lucy, and Rachel ride the bicycle together crooked, they like going "fast and faster." past their neighborhood. Perhaps this relates to Esperanzas, desire to get out of this neighborhood, because her life is tied to this neighborhood.