Reply to "spiral-curve-spiral"

I used atlas O flex track which is by its nature difficult to bend.  I just put in enough bend to make the curves work in the space I had so it pleased the eye.  No formula, just get the broadest curve with the space.  I was also able to incorporate a couple of small deviations from straights along the front of the layout where it is visible. This slight change in direction from straight running I find pleasing to the eye especially with the longer equipment. The Atlas O bends smooth without a worry of a line.