In small saucepan cook vinegar over low heat until reduced to about 3 tablespoons and vinegar is syrupy.
In small bowl stir together thyme, garlic, peppercorns, and salt. Rub on both sides of steaks.
Coat grill rack with nonstick cooking spray. Preheat grill to medium direct heat. Grill steaks, uncovered, to desired doneness, turning once halfway through grilling. (Allow 11 to 14 minutes for medium-rare or 13 to 16 minutes for medium).