How many engines are needed to make the grade?

[dtrainBNSF1]

I'm not sure what you mean by "tell a coal car to act like a loaded box or tank car". Wouldn't that be done by going into the bin files? I know that in the locomotive's bin file located in the Engine folder that you can change the location of where it gets its physics from in the SimulationContainer section (or something like that) but I'm not sure you can do that with an individual car.

[Ericmopar]

American coal cars and low side gondolas definitely behave different than a box car or tanker for instance.
The coal cars and gondolas tip to easily, and essentially behave as if there is little or no mass on a grade.

Box cars, tankcars, autoracks, flatcars, passenger stock etc all behave in a reasonable way in terms of number of engines and how they behave on a steep grade.

The different types of cars are definitely drawing on separate instructions on how to behave when loaded.

A person can build a 70 car coal train and load it, then drive it up a 1.5% grade with two SD70 with no problem.

Build the same 70unit train with 16,000gal tankers in the loaded state, and those same two SD70 might not make it up the 1.5% grade at all. Certainly if they do, they will struggle with the load.

The Tankers, Steel Roll cars and others will require similar loco numbers and type for a given grade, to the prototype.

I should also add that the low side gondolas and coal cars behave okay when unloaded. Just not in the loaded state.

[dtrainBNSF1]

Ahhhhh. Gotcha Maybe that's why sometimes when I build a coal train some of the cars are tilted for no reason.

[Ericmopar]

Ahhhhh. Gotcha Maybe that's why sometimes when I build a coal train some of the cars are tilted for no reason.

Exactly, one of the problems associated with the coal cars and gondolas is consist tilt but changing the center of gravity in the bins doesn't seem to help on those cars.
I've wondered if the CG is tied to the actual load all the way at the top of the car.
If a person changes the mass for gondolas and coal cars to something between 80 and 120 they start to behave correctly when loaded, but are a bit heavy when not loaded.