Is it better to make a 180 degree turn of 18" radius HO track using a 22" easement at the start and end, or to simply make the entire half circle using only 19 1/4" radius pieces? That is, is it better to use an easement, or to simply make the turn using the larger radius track (I'm assuming that the 19 1/4" tracks are equal in area to the two 22s and four 18s make.)
Also, would the decision change if the curve was 270 degrees, as opposed to 180? Thanks!
-aka
They're apples and donkeys. Wider curves are always going to improve looks and handling, but the tighter curves, especially if traversed by speeding rolling stock of a length, are always going to do better if they are eased. So, it isn't really an either/or question. If you were running typical trains on a layout and had no curves tighter than 36" radius, easements would not be very important except perhaps to the purists or more finnicky modelers. For mechanical reasons, they would not matter any more than super-elevation. But if you are in the under 22" region and wanting to run longer items, then easements come into their own, particularly if you hope to thunder through at any great speed.
In the range you describe, up the radius every bit you can, and provide an easement of some sort to add cheap insurance.
Unless you are happy with the toy-train lurch at the point where tangent becomes curve, it is always better to use an easement.
That said, one section of 22" radius track is hardly an easement. To be useful, a single-section easement would have to be > 30" radius.
I dimly recall an article in MR that described a modeler who eased 24" radius curves with, I believe, successive segments of 36" and 72" radius, each slightly longer than a standard passenger car. Using the same basic formula on an 18" radius curve, you would need segments of 27" and 54" radius, each the length of the longest piece of rolling stock you plan to run.
As for me, I prefer to form proper spiral easements with flex track.
Chuck (modeling Central Japan in September, 1964)
I've tried using progressively decreasing radius sections to form a sort of "faux easement" and it does improve the looks, and maybe operation a wee bit. The whole concept of an easement is to transform tangent track into a curve of given radius in our case. That is to say the easement begins as a curve of infinite radius. Flex track does the job, and in less space. John Armstrong's book gives good instructions on this matter, and the Paul Mallery book gives the actual equation for a cubic spiral (!) and templates if you want to go there.
The point is that an easement is a spiral; there is no sudden change of curvature. Easements will take less space than faux easements, and will materially enhance operation. They are worth using on any mainline trackage. Guess that's why I like to switch! Have fun!