curve minimums

Some of the RoW I have seen lately got me wondering how tight a curve a narrow gauge b class two truck geared locomotive would have been able to negotiate. A previous post on this site stated that b class shays have a turning radius of 75-100 feet depending on model, c class shays have a 100' radius. The post made it seem as if these are standard gauge specifications. How much could a narrow gauge shave off those numbers? There are logging lines I have been to multiple times that I still don't know if trains simply traveled around a sharp curve or would have needed to make a switchback.