RoyBoy on "tag page"

Hi
my tag page isn't working with wp_query()

I decided to get the tag from the querystirng:
$tag = basename($_SERVER['REQUEST_URI']);

and then query by taxonomy:
$args = array('post_type' => 'post','tax_query' => array(array('taxonomy' => 'tag','field' => 'slug','terms' => $tag)));

Have searched the forums but can't seem to find anything

Any suggestions?

Cheers