Don Merz 070317 posted:In another topic on the forum, a member is wondering why 072 is required for a specific loco he is shopping for. I have often wondered about the issue of curve requirements. Correct me if I am wrong, but as the required curve goes up, sales of that engine or car set must go down, right? Because fewer layout owners have layouts with those big curves., right? If that is true then manufacturers must have a strong incentive to make their gear run on the tightest of curves. Or maybe the collectors who never run their gear make up for the lost sales?
It bugs me sometimes when I see, for instance, a SHAY that requires 072 curves. What the heck? The prototype was designed to go around a dime and give you 9 cents change. Now the model needs (what I consider to be) luxurious, mainline curves? I don't get that.
Does the issue relate to scale versus traditional or near-scale? Is it the swing of the trucks? The overhang of the ends of the machine hitting tunnel portals and other track-close stuff?
Most of my layout is limited to 054. I am in the process of including 2 loops of 072 just so I can run some of the beautiful 072 models. But I won't dare let the 072 guys stray into 054 territory when this is done. And that leaves out most of my track plan.
So anyway, I know this isn't world politics and I am just whining. But I'm curious to know what is driving the need for big curves when the sales incentive would seem to go the other way.
Don
Well, what you perceive should be happening is not necessarily what really is happening. A misperception. Don't feel bad, happens to me sometimes, too.
Depends what size of prototype you are talking about. The largest Shays and other geared locos needed a fifty cent piece to go around and only gave back 4 or 5 cents in change.
One other thing to think about, O72 curves, while you may think they're generous, are pathetically small compared to the prototype. O72 curves translate into 144 foot prototype radius, and most full-sized locos couldn't even begin to operate on curves that small. If a manufacturer produces a large, scale-sized loco and says it needs O72 minimum, we better thank our lucky stars we can run it on curves that small! 
