public PhysicsCollisionObject getGroundObject() {
        if (wheelInfo.raycastInfo.groundObject == null) {
            return null;
        } else if (wheelInfo.raycastInfo.groundObject instanceof RigidBody) {
            System.out.println("RigidBody");
            return (PhysicsRigidBody) ((RigidBody) wheelInfo.raycastInfo.groundObject).getUserPointer();
        } else {
            return null;
        }
    }
returns the object this wheel is in contact with or null if no contact
@return the PhysicsCollisionObject (PhysicsRigidBody, PhysicsGhostObject)
jme3-jbullet/src/main/java/com/jme3/bullet/objects/VehicleWheel.java