1Spray inside of 4- to 5-quart slow cooker with cooking spray.
2Remove inner skin from ribs. Mix brown sugar, salt, pepper, liquid smoke and garlic; rub mixture into ribs. Cut ribs into 4-inch pieces. Layer ribs and onion in slow cooker. Pour cola over ribs.
3Cover and cook on low heat setting 8 to 9 hours or until tender. Remove ribs from slow cooker. Drain and discard liquid.
4Heat coals or gas grill. Place ribs on grill. Brush with barbecue sauce. Cover and grill 4 to 6 inches from medium heat 15 minutes.