Is the minimum radius curve spec for something like the Big Boy and other large locos, more to do with interference on parallel tracks, or it will derail or bind up on anything less than the 72 inch minimum radius?
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It's a binding / truck derailment issue. Also, for O gauge, curve measurements are diameters. Generally it's center rail to center rail, but original Lionel O track you might see listed as 31", but that's from outside tie edge to outside tie edge. Fun, huh? As far as concentric curves and scale sized steamers go, the general consensus here is 5-6" between tracks, which then means curve diameters stepped 10-12".
Not that this is an original thought, but:
One of the funny things about 3RO "radius" (like 031, 042, etc) is that it actually is diameter, not radius. Almost all other formats of model RR'ing use the radius as an expression of curvature - as in 18" radius HO track, which in 3RO would be "036", and so forth. This diameter business seems to crop up in gauges/scales with a deep "toy train" heritage, as opposed to HO, N and the like.
A thought a bit off topic, yet related: MINIMUM RADIUS/DIAMETER (Whatever LOL)
Just because any engine or piece of rolling stock may travel through a curve doesn't mean it will look realistic doing so.
I observed an O Scale big boy traveling through a 54 diameter/27 radius curve. It made it and gave me a good belly laugh! Wow! Don't run it too fast through there I thought.
Do you want your train to look like a train or the wild mouse at Coney Island? The broader you can make any curve the better! Yes, we all face space constraints. Compromise is king again because you may have to choose between appearance and function, unless they will lease you the Superdome for your layout! LOL
Any train, any scale, any gauge, will look more realistic on broader curves and operate, run more smoothly, as well..
Another factor in this minimum radius discussion that gets passed over too often is the functionality of a large locomotive on too-tight curves. A large locomotive may traverse the curves by itself, but try coupling a freight or passenger car behind it and see what happens. That rear overhang will pull that car right off the tracks if the curve is significantly too tight.
@CALNNC posted:Is the minimum radius curve spec for something like the Big Boy and other large locos, more to do with interference on parallel tracks, or it will derail or bind up on anything less than the 72 inch minimum radius?
I can tell you for sure the VL-BB locomotive will actually make it around an O60 curve, but the tender with the centipede wheels derails on the O60 curve.
Thanks for the replies and info. The only hobby shop here in town has a nice O gauge layout with I think 63 outer, 54 inner curves, all Gargraves or Atlas, but he never had a large loco like a Big Boy to try on it. Even as an authorized MTH and Lionel dealer, he never could get any of them in to sell.
