Also depends on the equipment. Diesels are more forgiving than Steamers. Rolling stock can be a toss up. The longer the car (like passenger cars) the larger radius they will need. Low hanging details, tanks, electrical boxes, etc., will often hit switch machines if the radius is too tight.
I'd do some mock ups and test what you want to do. Especially test a pair of switches back to back and see how the engines/ cars handle the S curve.
I've found most equipment can tolerate one size down from the spec'd rating, (eg- an 054 engine will handle 042 curves)
Bob
