The belt should fit in the groove tightly. If you show no wear in the bottom of the pulley then maybe the belt is too wide. It should go all the way into the pulley groove and show contact from the top to the bottom without bottoming out. In other words the belt angle and width should be the same as the pulley. General example, a 1/2" belt will work on a 7/16" pulley but still won't fit right.