Need to know a minimum radius to run a Sunset 3rd rail Baltimore and Ohio 
Q4b.
Robert Helm
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Hey I know that layout. Lol.
It should be 54" minimum.
I'd be surprised if it wouldn't go 48" or tighter. A friend has one and I've been itching to do some min. radius tests on his stuff anyways. Perhaps we'll have a definitive answer for you soon. In my experience 3rd rail is quite conservative on most of their posted mins.
I would suspect the minimum would be 54" if it's consistent with the 2-rail H1 Sunset/3rd Rail produced (I considered buying one). Note that sometimes the minimum radius isn't about what the locomotive will get through, but whether it will get through coupled to something else.
I have a USH PRR L1 Mikado. It has a pretty rigid frame, and all drivers flanged and 62 inch drivers. it will go around 48 inch radius. I don't know how tight it will go.
It has a fairly short tender as tenders go, and it will easily stayed coupled on not cause any problems on those curves.
So my guess is there is a good chance the SS loco will do the same. My experience with SS locos is that they have more driver sideplay than USH.
My minimum on my layout is 54” but I have a friend who also has the Q4b and his minimum radius is 50”. He doesn’t have any issues with it.
