Very nice example and code for using Box2D to create a vehicle and some easy customizations. Making monster trucks or skateboards!
Link: Creation of a Box2D car with 10 customizable parameters – (http://www.emanueleferonato.com/2011/09/18/creation-of-a-box2d-car-with-10-customizable-parameters/) from (author unknown) at Emanuele Feronato
