SilverStripe Setting Menu Title

class UpgradeNotificationPage extends LeftAndMain {

	static $url_segment = "upgrade";
	static $menu_title;
	static $menu_icon;
	static $menu_priority = 1000;
	static $allowed_actions = array ('upgrade', 'refresh');

	public function init() {
		self::$menu_title = 'foo'; //why doesn't this work?
		self::$menu_icon = 'bar'; //why doesn't this work?
		parent::init();
	}