What's the reasoning behind all the variations steam locos had with their lead and trailing trucks. (ie 2-6-2, 4-6-2, 2-6-4) I understand about the number of drivers and the need for power and traction, and that lead and trail trucks helped guide the loco but why the differences? If more axles on a truck is better, why not go with 2 or 3 instead of 1 axle? It shouldn't have added that much weight, should it? And why would one railroad but several versions of the same "base model?" For example, ATSF had 2-8-2 Mikados and 4-8-4 Northerns. Is it because that's what the manufacturer had in production? Just trying to expand my knowledge, which will eventually lead to an expanded inventory. Thanks!