Stringlining Calculator

On a sharp curve, a long car under tension can get dragged straight across the inside rail — “stringlining.” Set your tightest curve and longest car to see the risk. Works for a flat curve or a helix; the radius is all that matters.

A lighter or longer car stringlines first — weight light cars to NMRA RP-20.1, and cut head-end pull with a helper (see the Grade Pull calculator). This is a first-pass heuristic; confirm a marginal curve by running your longest car. More on the forces in the glossary.