Get low and tight under the tire, hands placed wide on the inside lower edge. Your hips should be lower than your shoulders, chest up. Hug the tire, don't push it away. Drive through your legs, extending up and through the tire, and roll it forward by flipping it end over end. The key is the entry — if you start too upright or don't get your hips low enough, every flip becomes a deadlift instead of a hip drive. Nail the setup and the tire almost flips itself. Get it wrong and you'll feel it in your lower back for all the reps.