Gradients are an essential part of any larger model railway layout. A layout without any rising and falling sections of track can look a little too flat and be operationally boring if you’re not careful. But getting the gradient right is very important indeed. Too shallow and you’ll need a very long run to get the track high enough to cross over another track or road at a realistic height. Too steep and a locomotive hauling a rake of loaded wagons or coaches will struggle to climb the length of the gradient. This results in wheels slipping and unnecessary strain being put on the locomotive, which can ultimately result in the motor burning out.
So the steepest gradient you can use on a model railway layout depends on several factors:
- The scale of your model
- The weight and power of your locomotives
- The length and curvature of your track.
As a general rule of thumb, a 3% gradient (or a rise of 3cm per 1 metre of track) is probably the steepest you could risk to ensure smooth operation and prevent derailments.
For heavier locomotives or longer trains, a shallower gradient of 2% or 2cm per 1 metre of track, would make a more sensible choice to prevent excessive strain on the locomotive’s motor. Additionally, if your track includes curves, you may need to use a shallower gradient to compensate for the centrifugal forces generated as the train navigates around the curve.
On smaller branch lines and narrow gauge layouts it is possible to get away with slightly steeper gradients, up to 5% or 5cm per 1 metre of track and the trains you’ll be running will often be much shorter and lighter in comparison to the locomotives available power.
As always, it’s important to test your track fully before fixing it down permanently. Run your fully loaded trains up and down the gradients and particularly around curves at the maximum speed you expect them to be run to make sure everything runs smoothly. Persistent derailments due to a poorly planned curve on a gradient will soon become a major frustration.
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Keep on shuntin’
The whole train is trying to overcome rolling friction. As soon as the locomotive starts climbing, it has to overcome the rolling friction and defeat gravity – as each wagon/coach starts it’s climb it adds more climbing load until the whole rake is climbing – and there can become a point when the total load on the locomotive defeats the traction friction grip of the locomotive’s wheels. Rolling friction increases on curves, the tighter the curve the greater the rolling friction, because the inner wheels are being dragged around the inner rail – best to have no curves on a gradient.
Even some recent railcar sets from a well known manufacturer struggle on a 3% gradient, not enough traction.