I've seen some discussion, but none of it authoritative.  Bought a Spectrum Shay years ago waiting for the day when I'd get a layout back up again in new house, and now that basement finished am ready to go.  Trying to plan a separate section of the layout with logging terrain to run the Shay, and I can't find anything authoritative from Bachman in the instructions or online about the min. radius.  I see discussion in 2010 but it was all anecdotal with people saying what they're successfully running Shays and some other locos on.  I see 18" ok.  But I'd think with the Shay design it should be able to turn a tight radius and I'd like to know for sure before I make the platform where it will be.  I could really use a diameter of 30" to squeeze turn into tight space - Is there anything authoritative or any user experience about whether will run on 15" radius?