INPUTS
Setups are saved in this browser only (nothing is uploaded).
Example: 2.0 means a 2% incline
Used in Feasibility & Max grade modes
Typical ~3.5–5.0 oz (100–140 g). This is a generic average, not an NMRA figure — NMRA RP-20.1 sizes weight per car length.
Measure w/ scale: pull until slip, record peak
Maps to a coefficient R (dimensionless)
Helix mode derives grade from radius + rise/turn
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Grade + curve-equivalent grade
General track settings
Adds an equivalent grade (≈ 32 / radius in inches, the accepted HO rule of thumb)
Adhesion cap (limit pull by weight on drivers)
If unknown, leave 0 and the cap is ignored
Typical clean metal-on-metal is ~0.2 – 0.35
Stringlining (lateral pull on curves)
Truck-mount generally reduces stringlining risk
Use body length (approx). Set 0 to disable
Uses the helix radius, or the radius implied by your curve preset in General mode.
Custom rolling resistance (override the preset)
Lower is better rolling. Try 0.003 – 0.010
Calibration (optional but makes results real)
Drawbar pull: On straight, level track, attach a string to the coupler and pull against a digital scale (or spring scale). Increase until the wheels just begin to slip; record the peak.
Rolling resistance: If you can measure “pull to keep moving” for one car on level track, you can back-solve R. This MVP doesn’t include the wizard yet, but the custom R box lets you dial in your fleet.
This tool is an approximation.
RESULTS
Max cars
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Per Car Resistance
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Drawbar Pull vs Number of Cars
| Component | Per Car | At N Cars |
|---|---|---|
| Grade | — | — |
| Rolling | — | — |
| Curve penalty (extra) | — | — |
| Total required | — | — |
| Available (drawbar) | — | — |
Model: Required pull per car = carWeight · (grade% + curveEq% )/100 + carWeight · R. Curve resistance is treated as an equivalent grade using the accepted HO rule of thumb curveEq% ≈ 32 / radius(in).