Preheat grill for indirect cooking over medium high heat. Place drip pan under the food. Mix beer, sugar and pepper in a foil pan centered on grate. Brush brats and onion slices with oil and grill over coals on either side of foil pan until nicely browned, turning once. Place brats and onion slices in the beer mixture, cover pan with foil and continue cooking for 20-30 minutes or longer.