Make sure you.include one car in experiments into undersized curves. I have two that can make tighter than designed curves ...ALONE . Cars get dragged off because of pilot overhang/coupler ends up traveling wide too, and the angle between 2 couplers binds before the angle of the turn is reached.
On those locos, to run in the tight curves, my lead car will have an articulated coupler shaft like on passenger cars. The articulated pivot point is moved towards the coupling point relieving some of the angle at the couplers.
