So, I have two racks of pork spare ribs, sitting in their rub, in my fridge. I plan to cook them on low heat tomorrow for dinner with guests. In the past, I have always cooked baby backs, but my husband wanted spare ribs this time. I intend on cooking them on the grill - thankfully NYC weather will cooperate tomorrow. So, I will be cooking them on low heat, but how long for spare ribs?????