Dry Rub. In a small bowl, combine brown sugar, black pepper, garlic powder, and paprika. Whisk until well blended. Pat ribs dry with paper towels and coat the tops with spice rub. If you have time, you can apply this dry rub up to 1 day in advance. (Keep ribs covered in the refrigerator until you’re ready to use them)
Layer & Add Sauce. In a small bowl, whisk together 1 cup of the barbecue sauce with 2 Tablespoons apple cider vinegar. Place one half of the rack of ribs into the crock of your slow cooker. Cover with 1/2 cup barbecue sauce/vinegar mixture. Add the second half of the ribs and cover with 1/2 of the barbecue sauce/vinegar mixture. Pour 1/2 cup of water into the bottom of the slow cooker.
Cook the ribs on LOW 7-8 hours or HIGH 3-5 hours. My favorite is about 4 hours on HIGH, which gives the ribs a fall-off-the-bone texture. If you like your ribs a bit more chewy or sturdy, you can pull them out closer to the 3 hour mark.