QUOTE(sixman @ Mar 8 2007, 12:41 PM)
Coke also weighs less than coal, so the hoppers for coke transport will have a high cubic foot capacity.
Correct. What that translates into in terms of making accurate models is that, for example, a 70 ton capacity hopper may be loaded to capacity with gravel, and yet be filled only two-thirds of the way to the top of the car. Or, a 70 ton capacity coal hopper filled all the way to the top with coke may not actually be filled to capacity. If an ordinary coal hopper is converted to carry coke it is not unusual for the sides to be built up higher so that it can carry its full capacity.
Back before aluminum cars, when typical large sized hoppers were 70 ton nominal capacity, in round numbers the empty car could weigh 66,000 lbs and could carry 154,000 lbs of payload. If for some reason they could only put 140,000 lbs of payload into the car, then ten percent more cars would have to be moved. At 66,000 lbs empty weight per car, plus eight solid bearings per car, the railroad would do well to modify the cars to get the payload up to the limit!