Grade and train length

What is checked? Whether your train can climb the ramp. The tractive effort of the locomotive — limited by the adhesion of its wheels — is weighed against the resistance of the whole train: rolling resistance of every vehicle, the grade under every vehicle and curve resistance. The train is pushed through the whole ramp, along every passable turnout route and uphill in both directions; the least favourable position counts. The ★ train of your train profile is checked (all trains if you wish). Without trains of your own the check uses a substitute train built from the train length: a freight train with a diesel and box cars, a long-distance train with an electric loco and coaches, a local train of railcars.

Why does it matter? Train length and feasible grade are directly linked: every car and every percent of grade costs tractive effort. A single loco makes it up a steep siding, the whole freight train fails on the same ramp. And model locos start to slip at about half of their measured maximum pull — so a ramp only counts as safe when half of the tractive effort stays free. Rules of thumb for H0: a loco on its own manages 4–5 %, ten short freight cars are fine at 2–2.5 %, ten coaches at 2.5 % only just, and with 15–20 coaches you had better stay below 1.25 %.

How to fix it: The finding names two numbers: how many cars make it up safely and to which grade you would have to ease the steepest parts. Other ways: a second loco (double heading or a banker), a loco with traction tyres or a heavier loco. Next to the “Grade” check, which measures against the limit of your plan, this check tells whether your train makes the climb — both findings can sit at the same place.

Numbers & defaults: “Safe” means with 50 % reserve, below that “only just” (warning), without reserve “too steep” (error). Friction coefficient 0.12 without and 0.30 with traction tyres, rolling resistance 2 % (garden railway 3 %). Car weight from the length over buffers per NEM 302 (H0 0.40 g per mm, 0.45 g with a practical allowance), loco weight by loco type (H0 diesel and electric 450 g). Curve resistance after John Allen, converted to the track gauge. Traction tyres: yes for European, no for US track systems. These are estimates with a wide spread — your own measurement in the train profile (“my loco pulls at most N cars up X %”) makes it more precise.