r-a-y

function redirect_to_forum() {
    global $bp;

    $path = clean_url( $_SERVER['REQUEST_URI'] );

    $path = apply_filters( 'bp_uri', $path );

    if ( bp_is_group_home() && strpos( $path, $bp->bp_options_nav['groups']['home']['slug'] ) === false )
        bp_core_redirect( $path . $bp->bp_options_nav['groups']['forum']['slug'] . '/' );
}
add_action( 'wp', 'redirect_to_forum' );