I remember from a video on steamers some time ago. It had DRGW cars that had strange wheels. I went to RailPictures.net entered Ski Train and found this:
IIRC, these cars were purchased from VIA Rail in Canada. These were standard passenger cars built for CN and CP, just can’t remember who built them(Pullman Standard or Hawker-Sidley come to mind, just not sure…)[?]
My guess, and that is exactly what it is a guess, is that the disk brakes are for the grades in the mountains. I would think that they would want as much braking as they could get for those heavy cars up in the hills.