Preheat oven to 275°F. Slide a knife under each rack's back membrane; pull off with paper towel.
Mix brown sugar, paprika, chili powder, garlic powder, onion powder, salt, pepper, and cumin in a small bowl.
Rub generously over both sides of ribs; wrap each rack tightly in foil.
Place on baking sheet; bake 2.5 to 3 hours until very tender and pulling from bones.
Meanwhile, whisk barbecue sauce, vinegar, and honey in a small saucepan over medium until combined and warmed through.
Remove ribs; carefully unwrap. Preheat broiler or grill to medium-high.
Brush ribs generously with sauce; broil or grill 3-5 minutes until caramelized and sticky.
Rest 5 minutes; cut between bones and serve with extra sauce alongside.