[Solved] Redirect Issue Codeigniter

PHP Code:

redirect("forum/$forum_id"); 


It worked like

PHP Code:

redirect('forum/' . $forum_id); 


For some reason works on site_url('forum/') . $forum_id but not redirect('forum/') . $forum_id;

There's only one rule - please don't tell anyone to go and read the manual.  Sometimes the manual just SUCKS!