In a large bowl, combine the vinegar, water, oil, thyme, sugar and salt and pepper to taste. Add the steaks, mixing well, and let marinate in the refrigerator for 6 to 8 hours.
Prepare an outdoor grill with an oiled rack set 6 inches from the coals. On a gas grill, set heat to medium.
Remove steaks from the marinade and reserve the marinade. Grill 14 to 20 minutes for rare, 20 minutes for medium, or 26 minutes for well done, brushing with reserved marinade. Remove from grill and carve into thin slices.