What do GVWR and GCWR mean when towing?

GVWR, the gross vehicle weight rating, is the maximum the vehicle itself can weigh fully loaded with passengers, cargo and tongue weight. GCWR, the gross combined weight rating, is the maximum for the vehicle and loaded trailer together. Staying under both, plus the towing and payload ratings, matters for braking, handling and safety. These figures are in the owner's manual and on the door-jamb label.