@Override
    public void read(JmeImporter im) throws IOException {
        InputCapsule capsule = im.getCapsule(this);
        wheelSpatial = (Spatial) capsule.readSavable("wheelSpatial", null);
        frontWheel = capsule.readBoolean("frontWheel", false);
        location = (Vector3f) capsule.readSavable("wheelLocation", new Vector3f());
        direction = (Vector3f) capsule.readSavable("wheelDirection", new Vector3f());
        axle = (Vector3f) capsule.readSavable("wheelAxle", new Vector3f());
        suspensionStiffness = capsule.readFloat("suspensionStiffness", 20.0f);
        wheelsDampingRelaxation = capsule.readFloat("wheelsDampingRelaxation", 2.3f);
        wheelsDampingCompression = capsule.readFloat("wheelsDampingCompression", 4.4f);
        frictionSlip = capsule.readFloat("frictionSlip", 10.5f);
        rollInfluence = capsule.readFloat("rollInfluence", 1.0f);
        maxSuspensionTravelCm = capsule.readFloat("maxSuspensionTravelCm", 500f);
        maxSuspensionForce = capsule.readFloat("maxSuspensionForce", 6000f);
        radius = capsule.readFloat("wheelRadius", 0.5f);
        restLength = capsule.readFloat("restLength", 1f);
    }
returns how many degrees the wheel has turned since the last physics
step.

@return the rotation angle (in radians)
jme3-jbullet/src/main/java/com/jme3/bullet/objects/VehicleWheel.java