Reply to "Understanding track spacing on curves"

I am testing 88, 84, and 72 as my triple main on my 18.5 by 10 foot layout. I am starting with 5.5 to 6 inch center rail spacing.  I plan on screwing down the outside track first.  Using my Big Boy, Allegany and EM1 I will add the inner loops and testing before I finalize the inner loops. I will also assure spacing for the 21 inch diner cars during that process.  I will also need to determine the location of the steel tread dowels I will need to support the 2nd level.  As others have said, the spacing is dependent upon track geometry and type of engines and rolling stock you plan to run on the layout.  Start with an assumption that either 4.5 or 5.4 inches will work and adjust accordingly.