In a small bowl, combine 2 tablespoons salt, 1 tablespoon black pepper, the brown sugar, coffee, garlic, chipotle powder, and red pepper flakes. Pat the steaks dry with paper towels, place them in a baking dish, and rub them all over with the olive oil. Rub the steaks on both sides with the spice mix, using it all. Cover the dish and refrigerate for at least 2 hours to allow the flavors to get into the meat.
When ready to cook, heat enough charcoal to cover half of the grill (I fill a charcoal chimney 3/4 full). Pour a layer of hot coals on one side of the grill, leaving the other side empty.
Cook the steaks on the hot side of the grill for exactly 2 minutes on one side, turn them over, and cook for exactly 2 minutes on the other side. Move the steaks to the cool side of the grill, put the lid on, check to be sure the vents are open, and cook for 8 to 10 minutes, until an instant-read thermometer inserted sideways into the middle of the steak registers between 115 and 120 degrees for medium rare and 120 and 125 degrees for medium. Transfer the steaks to a plate, cover the plate tightly with aluminum foil, and allow to rest for 15 minutes. Remove the foil after 15 minutes or the steaks will continue to cook. Slice the steaks, sprinkle with salt, and serve hot or warm.