Zoom! by Robert Munsch.

Finally it's time for Lauretta to get a new wheelchair. But she isn't satisfied with a regular 5- or 10- speed model. Nothing will do but the 92-speed, black, silver and red, dirt bike wheelchair! When Lauretta gets a speeding ticket during her one-day tryout of the super wheels, her parents tell her the wheelchair has to go back. But when her brother has an accident, only Lauretta and her 92-speed, black, silver and red, dirt-bike wheelchair can get him to the hospital in time!