Radius Size?

Bigger is always better when it comes to radius...! You can always have parts of the layout "off-limits" to the BigBoy, just as was done in the real world. Let the little 0-6-0 handle the industrial switching on sub-11 inch curves, and let the BigBoy run out on the main with 11/15/?? curves.

Andrew
 
Charles,I would go with the largest curves possible for long wheel base locos like that Big Boy and long wheel base cars like passenger cars.You won't regret it farther down the line in smooth operation of your trains as they traverse your layout.
 
You could always contact the manufacturer and find out what is the minimum radius they recommend.
Another approach, and IMO the best, is to lay out a test track of the radius you want to use and run your engines thru the curve. This is good for grades as well.

Val
 
I've decided to widen the one curve that I am concerned about. No track has been laid. I bought another set of WS inclines yesterday so will correct the possible problem now. I'm learning as I build for sure.