For rub: In a small bowl, combine brown sugar, paprika, salt, garlic powder, dry mustard, celery salt, and cayenne pepper.
Sprinkle rub evenly over ribs; rub in with your fingers.
In a smoker arrange preheated coals, wood chunks, and water pan according to manufacturer's directions.
Pour water into pan. Place ribs, bone side down, on grill rack over water pan. (Or place ribs in a rib rack and place on grill rack.)
Cover and smoke for 2 1/2 to 3 hours or until ribs are tender, brushing once with the Kansas City Barbecue Sauce during the last 15 minutes of smoking.
(If ribs get too dark, wrap in foil during the last part of grilling.) Add additional coals and water as needed to maintain temperature and moisture.
Serve ribs with remaining sauce.
Kansas City Barbecue Sauce
In a medium saucepan cook onion and garlic in hot olive oil until onion is tender. Stir in apple juice, tomato paste, vinegar, brown sugar, molasses,
paprika, Worcestershire sauce, salt, and black pepper. Bring to boiling; reduce heat. Simmer, uncovered,
about 30 minutes or until sauce is desired consistency, stirring occasionally. Stir in horseradish.