About one hour before smoking, make the dry rub. Combine 1/4 cup brown sugar, garlic, chili powder, kosher salt, 1 teaspoon black pepper, 1/2 teaspoon cayenne and coriander in a small bowl. Pat ribs dry with paper towels; sprinkle both sides of each rack with the rub. Set aside at room temperature for 1 hour.
Heat charcoal or gas grill for indirect cooking at 250 degrees F. to 300 degrees F. Add drained wood chips, if using.
Place the ribs, meaty side up, over a drip pan and cook 2 hours. Add about 12 coals to a charcoal grill every 45 minutes or so to maintain the heat.
Meanwhile, to make the sauce, combine vinegar, honey, ketchup, remaining 1/4 cup brown sugar, paprika, sea salt, remaining 1/2 teaspoon pepper and 1/4 teaspoon cayenne in a medium saucepan over medium heat. Bring to a boil; reduce heat and simmer 15 minutes, stirring frequently, until lightly thickened. Set aside to cool to room temperature, then refrigerate.
Continue cooking ribs 1 to 2 more hours until very tender, spraying on both sides with apple juice every 20 to 30 minutes.
Brush ribs with sauce; continue cooking for about 5 minutes, until the sauce is set. Turn ribs and repeat with more sauce.
Cut the racks into 3- or 4-rib sections and serve. Pass any remaining sauce at the table.
