Sleeping objects behave differently than Flash version

Happy Wheels iOS uses a version of the physics engine Box2D which has been updated since the release of the original Flash game. Sleeping bodies behave quite differently. In Flash, bodies must contact each other to wake from sleep. However, In iOS if two bodies can collide, only the bodies’ bounding boxes only need to overlap. A bounding box is basically a rectangle that encloses your object. A bounding box can be much larger than an object's actual shape, depending on the object's angle.