1. In a large bowl, Add brown sugar, paprika, mustard, garlic powder, onion powder, cayenne pepper and coarse salt. Mix them well to combine.
2. Pour the cider vinegar and stir to make a smooth paste.
3. Rinse the pork spare ribs and pat them dry with a paper towel.
4. Using a knife remove excess fat and the hard membrane.
5. Place the ribs on a flat surface and rub the spice mix paste generously on both sides. Prepare all the slabs this way and place them in a wide mouthed dish.
6. Cover and refrigerated it for 2 hours or more.
7. Heat the grill.
8. Place the ribs on the grill. Sear them and transfer them on the upper rack to grill under indirect heat.
9. Grill them for 2 hours.
10. Brush the ribs with barbecue sauce generously and grill for another 20 minutes.
11. Remove from grill and allow to sit for few minutes.
12. On a serving platter, slice and serve them warm.