The curve on which the model is designed and developed using the factory-equipped couplers, is a UNITRACK 249mm (9-3/4”) ground-level curve for N scale models. For HO scale, the design curve is targeted as a UNITRACK R457mm (18”) ground-level curve.
If you are using a curve smaller than N249mm/HO457mm, you will have to determine for yourself if the model will operate satisfactorily on your layout. The solution may be as simple as converting to longer shank couplers (often provided with the model). The same determination will have to be made if you are using viaduct track. You may need to cut away or shave some height from the viaduct wall.
We will try our best to add specification to individual model pages on our web site if and when we learn from the factory or outside hobbyists where an exception to the above and/or a unique operating circumstance exists.