About one hour before you plan to start grilling, make the rub: In a small bowl, combine the chili powder, salt, garlic powder and pepper. Set aside 2 tablespoons of rub. Pat the ribs dry with paper towels, then sprinkle both sides of each rack with the rub. Set aside at room temperature for one hour.
For the mop, combine the vinegar, water, reserved chili rub in a bowl, mixing to combine. Set aside.
Preheat the grill for indirect cooking at 250 to 300 degrees F. Add the drained wood chips, if using.
Place the ribs, meaty side down, over a drip pan, close the grill, and cook for 1 hour, adding about 12 coals to a charcoal grill every 45 minutes or so to maintain the heat.
Continue to cook the ribs until they’re so tender and meat has shrunk from the bone ends by 1/2 inch, brushing both sides with mop mixture every 45 minutes, 4 1/2 to 5 1/2 more hours. Brush the ribs on both sides with the barbecue sauce and continue to cook for about 5 minutes, until the sauce is set. Remove from the grill and let stand for 5 minutes.
Cut the racks into 3- or 4-rib sections and serve.
Serving suggestions: Serve these ribs with cool and creamy cole slaw and twice-baked potatoes.