At the back of the C15 you find what I assume on the prototype is a radial truck. The model cheats and uses a pony track hidden in the frames to do the same job for a whole lot less engineering. It's a common enough subterfuge as no one can see the difference from the track side and saves trying to make a bent tube up accurately from soldered bits.
As well as swivelling, the truck is so narrow that there is a load of side play in the axle even with the bearing inserted from the inside of the box and protruding wheelward. I see a lot of spacing washers on the fret but think they can stay there for the time being - until I get to test this model on it's eventual home anyway.