Preheat oven to 325 degrees F. Place the ribs meat-side up in a roasting pan or casserole just large enough to hold them in a single layer. Combine chili powder, cumin, brown sugar, salt and pepper in a bowl, them sprinkle and rub into the ribs. Pour in beer. Cover and bake two hours, or until ribs are quite tender. Preheat barbecue to medium-high heat. Grill the ribs 2 to 3 minutes per side, or until nicely coloured. Brush with barbecue sauce and allow it to heat through before servings the ribs.