About one hour before you plan to start grilling, make the rub: In a bowl, combine all dry ingredients. Pat the ribs dry with paper towels. Remove the thin membrane attached to the underside of the ribs. Sprinkle both sides ribs with the rub. Set aside at room temperature for one hour.
Preheat the grill for indirect cooking at 250 to 300 degrees F.
Place the ribs, meaty side down, over a drip pan, close the grill, and cook for 2 hours.
Remove ribs from the grill. Double-wrap each rack in heavy-duty aluminum foil. Return wrapped ribs to the grill and cook until very tender, 2½ to 3 hours more.
Remove from grill, and allow to cool. Cut into slabs of 3-4 and serve.