Lots of good information posted here. Another rule of thumb for smooth-appearing passenger train running, is that the easement be at least as long as your longest passenger cars (15, 18, or 21 inches as the case may be). That’s the rule I’ve used, and at scale speeds the transition from tangent to curve appears seamless to my eye anyway.
I’ve used about 1/8 inch of superelevation from tie end to tie end. If you use super-elevation for curves, it should be done over the length of the easement at the minimum, watching for wheels lifting off the rail if trucks don’t have enough equalization. In this case I mean from front truck to rear truck, ability to tilt at the bolster, not axle to axle within a truck. If wheels are lifting enough that a flange can climb the outside rail, that would require a longer transition to super-elevation then. The curve easement length wouldn’t have to change. Only one maverick Lionel GP9 of recent manufacture has had that problem on my layout. Its identical mate except for road number has no problem.
I made a template using the ones printed in the Oct. 1969 Model Railroader article about easements, and eventually turned it into a sturdy thin plywood template could use to lay out curves. The offset with this is not extreme, less than the 1” mentioned above, so a 3/4 to 1 inch offset using the Armstrong lath method with such a rule of thumb for the length of the easement should have excellent results.
I could photograph my plywood template and post that. Probably these days you could copy and paste that and turn it into a scaled-up template, with the help of a commercial printer or laborious arithmetic and drawing it out. Or find a copy of the Oct 69 Model Railroader on eBay.
Fun stuff. Watching a favorite passenger train glide into an eased, superelevated curve is a great natural releaser of endorphins!
