How do railroads calculate engine numbers?

[Brickrail782]

I just recently started making long freight drags (100+ cars typically) in TS2017 and noticed a trend, the trains are easily able to climb a 2.0% grade, but the dynamic brakes don't do much to hold the train coming down the other side on a 1.0% grade. Is there some sort of "magic number" of engines needed for effective dynamic braking, or do trains often supplement dynamics with air?

[BNSFdude]

There's a maximum for total Rated Powered Axles and Dated Dynamic Braking Axles that varys from railroad to railroad and even per subdivision.

Dynamic Brakes very rarely will hold a train back entirely on their own on steeper grades, but it depends on trailing tonnage, really. So most of the time you'll have to use a minimum application with dynamic brakes at varying levels to control your speed.

The general idea is that if you have to use more than DB4 to hold a speed or even come to a stop, you should mix it with air to lessen your buff forces.

[Brickrail782]

Thanks for the info.