What's My Maximum Grade?
The largest manufacturer of model railroad landscape materials, Woodland Scenics, offers flexible incline foam for grading model railroad train layouts in grades of 2%, 3%, and 4%. If everyone followed the popular rule of thumb, I think it's safe to say that Woodland Scenics would not be selling 3% and 4% foam grade kits. As you can see from the diagram, these grades aren't very steep. But for real life trains, these are considered steep grades.
Track Grades: Prototypical vs. Toy TrainSome builders of prototypical model railroads will ridicule any grade steeper than 2%. And perhaps not without justification. In real-life railroading there are three classes of grades; 0.8% to 1% is "light grade", 1% to 1.8% is "heavy grade", and anything greater than 1.8% is "mountain grade". So perhaps it's not unreasonable to look askance at layouts with grades greater than 2% and call them "toy train" layouts. But that doesn't make it courteous... or kind. Maximum grade is frequently dictated by available layout space. I personally resent the implied requirement that if one is building a small layout it should be flat. I'll take a mountain grade railroad over a flat oval or figure eight any day!
Maximum Track Grade and Train IssuesSo just what is the maximum grade you can use? Maximum grade is a function of three factors: the power of your locomotives, the weight of your locomotives, and the number and weight of the cars in your trains. That the locomotive's power is a factor is common sense; a weak locomotive won't pull many cars up a grade. But how the weight of the locomotive's affects maximum grade isn't quite so obvious. The greater the weight, the greater the traction. This means wheels on lighter locomotives may slip where heavier locomotives can climb a grade. So larger scale locomotives may handle steep grades better than smaller scales. Good N scale locomotives can pull around 15 cars up a 4% grade. But to some modelers 15 cars is too short a train.
Grades, Like Curves, Are All About SpaceWith model train track curves our concern is the width of the space available to us. While curves can be used to break up the monotony of long straight sections of track, turning a train around with a 180 degree curve, a necessity for continuous running layouts, taxes the limits of a narrow layout.
With model train track, grades can also be used to make a layout more visually appealing. But interesting layouts frequently pass one track over another on bridges or trestles. And gaining sufficient height for an over/under on a short model railroad layout is where grades become a challenge.
Model Railroad Layout Overpass Clearances
Grading Runs for a Crossover
Split Your Track Grades
Curved Track GradesWhen you curve a grade you increase the effective slope of the grade. The tighter the curve, the steeper your effective grade. I'm not a physicist or a mathematician, so I can't give you exact numbers and equations to back them up. What I can tell you is that I know the physicists are right when they tell us this because I've proved it to myself.
I made an 11 inch radius curve with a 4% grade in N scale. My Athearn consolidation class locomotive would pull 9 of its Overton passenger cars over this curved grade with no difficulty. Then I made an 8.5 inch radius curve with a 4% grade. The consolidation would only pull 5 of its cars over this tighter turning grade. This grade was 1 inch high, half the N scale over/under height.
Multiple Unit Locomotive ConsistsWhen pulling longer trains, particularly in N scale, it is common practice to use the prototypical practice of pulling the train with multiple locomotives. This will also increase the size of a train that can be pulled up a grade, or the maximum grade for fewer cars. In the steam era it was not unusual for railroads to have "helper" locomotives standing by to be added to trains at steeper grades. While modern prototypical diesel trains usually put all the locomotives at the front of the train, I have seen modelers put locomotives in the middle of a train.
Ghost CarsAnother technique is to use a ghost car or "cheater car". This is a freight car, usually a boxcar, that is motorized like your locomotives. Ghost cars are usually put in the middle of a long train, or spaced evenly throughout a long train if more than one is being used. I haven't seen ready to run ghost cars in local hobby shops, but Randgust makes a ghost car kit and Reality Reduced has a video on how to put it together.
ConclusionsWhat I have learned about grades can be summarized in two statements:
Always build your layout on layers of foam with most track at the midpoint of crossover elevation. Then you can always split your grades going down for the under track and up for the over track.
When building a layout, before you glue down your grade foam and track always test your trains on the layout. Make sure your locomotives can navigate all your turns and grades, pulling whatever number of cars will be sufficient to ensure you enjoy the layout. If your favorite trains can't run on the layout, rethink your design. There's always a solution, but sometimes it takes a while to find it.
And remember, the point is to have fun.