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Radius planner
Why minimum radius is not one universal number
Manufacturers may publish minimum radii for individual products, but a complete train adds more variables: body overhang, coupler swing, truck rotation, adjacent-track clearance and S-curves. Treat any generic radius chart as a planning range, then verify your exact equipment.
Avoid the hidden S-curve
Two opposite curves with little or no straight track between them can force couplers sideways in opposite directions and cause derailments. A straight section at least as long as your longest car is a strong target when space permits.
Appearance versus operation
A train can sometimes physically negotiate a curve that looks unrealistic. Broader curves reduce overhang and make passenger equipment, articulated steam locomotives and long modern freight cars look much more convincing.