01 - Remove the tough membrane from the underside of each rack for optimal tenderness.
02 - Mix together brown sugar, paprika, smoked paprika, garlic powder, onion powder, black pepper, salt, and cayenne pepper in a small bowl until thoroughly blended.
03 - Evenly coat both sides of the pork ribs with the prepared spice mixture. Allow to stand at room temperature for 20 minutes to allow flavors to penetrate.
04 - Preheat a charcoal or gas grill to medium indirect heat, approximately 285-320°F.
05 - Tightly wrap each seasoned rack of ribs in aluminum foil, adding a splash of apple cider vinegar to each packet to maintain moisture.
06 - Place the foil-wrapped ribs onto the grill grate over indirect heat. Cover and grill for 1 hour and 30 minutes, turning packets occasionally for even cooking.
07 - Carefully remove ribs from the foil. Liberally brush barbecue sauce over both sides of the ribs.
08 - Return ribs to the grill directly over medium heat, uncovered. Grill for 10 to 15 minutes, turning and brushing with additional barbecue sauce until the exterior is sticky and lightly charred.
09 - Remove ribs from grill and let rest for 5 minutes. Slice between bones and serve hot.