To make dry rub, in medium bowl combine all ingredients for the rub and stir well to blend. Place ribs flat in a non-reactive roasting pan. Using 3/4 cup of the rub, sprinkle over both sides of each rack and rub in lightly. Set aside.
Soak wood chips in cold water to cover for at least 30 minutes. Set up grill for indirect cooking. Prepare a medium fire in a charcoal grill or preheat one side of a gas or electric grill on medium. Drain chips and sprinkle half over the coals or place half in the grill’s smoker box. Place a disposable foil pan under the grate to catch drippings.
Brush grill grate with vegetable oil. Arrange ribs, meaty-side down, on the side of the grill without hot coals. Cover the grill and smoke-cook the ribs for 45 minutes. Turn ribs and add remaining wood chips. Cover and grill for another 45 minutes.
While ribs are grill-smoking, make Hickory Barbecue Mop Sauce. Combine store-bought hickory barbecue sauce, liquid smoke, maple syrup and molasses in a bowl. Stir well to combine.
When the ribs have cooked for a total of 11/2 hours, brush the ribs generously with the mop sauce. Using long-handled tongs, slide the ribs onto the grate directly over the hot coals. Grill, uncovered, 5 minutes. Turn the ribs over, baste again, and grill another 5 minutes. Cut between the bones, slicing the racks into individual ribs. Serve immediately.