Thank you all  for your input.  I was confussed on radius, I have 11.5" radius using flex track.  I will keep that and add another track on the outside loop at a 19" radius.  My grandson is running a 4-8-2 Light Mountain and I also have a Northern 4-8-4 &52' Tender.  If I understand correctly these should run on a track that has a 19" radius and is 38" center to center of the rails.  excuse me if I get the terminology messed up as we just started this hobby or obsession. 

I just started building a layout with my grandchildren.  We started layting the track and were testing it as we go.  The 4-8-2 steam engine center wheels lift off the track as it goes around the radius.  The radius is 23 1/4".  In order to run any engine or car on the layout what is the minimum radius we can use.  Thanks