Make shallow cuts between the ribs on the bone side with a sharp knife, piercing just the membrane.
Mix 1 tbls salt, the brown sugar, garlic, thyme, chili powder, 1/4 tsp black pepper and the cayenne in a bowl.
Rub the spice mixture evenly over the ribs.
Place the ribs on a rack in a roasting pan, loosely cover and refrigerate at least 4 hours or overnight.
Meanwhile, combine the cider, ketchup, mustard and worcestershire sauce in a saucepan over medium heat and simmer until reduced to about 2 cups, abotu 30 minutes.
Cover and set aside.
Preheat grill to low heat on one side.
Cook the ribs bone-side down on the cooler side of the grill, covered, until tender, about 2 hours and 30 minutes.
Continue to cook, uncovering every 10 minutes to baste with sauce, until the ribs are glazed, about 40 more minutes.