Stand about two feet away from tire with a wide, staggered stance. Grip the sledgehammer, first with left hand at the bottom of the handle, and right hand closer to the head. Bring the sledge up, your right hand slides toward the head; as you swing down, your right hand will slide down to join your left hand. Slam it down as hard as you can against the tire. Repeat the sequence for all reps on one side then switch hands and repeat on the other.