In non-aluminum pan, combine spareribs with 2 cups root beer. Cover with plastic wrap. Refrigerate at least 8 hrs or overnight.
Preheat oven 325°F. Combine cumin, salt, garlic powder, onion powder and cayenne. Remove ribs from pan; discard liquid. Pat ribs dry; return to roasting pan. Sprinkle spice mixture over both sides of ribs. Roast ribs until very tender 1 hr 50 min.
Meanwhile, in a pot combine sugar and vinegar and rest of root beer; cook at high heat until reduced to 1/3 cup, 4-6 minutes. Remove from heat. Brush ribs with some of the glaze; Roast 5 min. Brush ribs with remaining glaze; Roast until deep golden brown about 5 minutes.