Pull off the thin membrane from the underside of the rack of ribs. Blot each rack of ribs with a paper towel to dry. Massage the spice rub into the ribs on all sides. Leave the ribs at room temperature for up to 1 hour before grilling.
Prepare a grill for indirect cooking by layering soaked wood chips and charcoal. When the coals are ashed over, spread them out in one part of the grill so the food can cook to the side and not directly over the coals. Cover the grill and bring it to between 225°F and 235°F.
Cook the ribs bone side down with the grill lid closed, for 2.5 to 3.5 hours, or until the meat just starts to shrink back from the ends of the bones. To ensure even cooking, set an oven thermometer next to the ribs.
Finish by basting the ribs on both sides with your barbecue sauce of choice, and placing them back on the grill for 5 to 10 minutes. Once completed, set the rib racks on a baking sheet and cover with foil; let them rest for 10 to 20 minutes, then slice and serve.