Michael -- We typically use 3" (16 prototype feet), often widened for sharper curves. Most prototypes use 13 feet, which is 2-7/16" in S. That's what I use on straight track except in yards, where I use 3" simply to get my fingers between the cars. All my curves are on 3" centers except in my staging, where my minimum radius is 33" on 3-1/2" centers.
Dick Karnes
