Gravity lanes look almost too easy, until production ramps and cartons start acting like different species. One SKU glides, another drags, and a third accelerates into the end stop. That inconsistency is rarely "operator error." It is rolling resistance, base rigidity, roller pitch, and transfer geometry colliding in real time. Over a week, those small stalls become a real throughput loss and fatigue. If sizing is treated as a controlled system, not a quick guess, the lane feels calmer and safer. In this article, we will discuss how to size slope, roller pitch, and control points for safer carton flow.