Compared to the S-1, the locomotives of the S-2 class received larger driving wheels with a diameter of 80 inches, as they were only intended for express trains. They also burned oil and now had cylinders measuring 29 by 29 inches. They showed up more than 50,000 pounds less on the scales thanks to a smaller boiler. Since the adhesive weight was also reduced as a result, the locomotives slipped more quickly when starting and had to be operated with great care. Nevertheless, from 1949 they were no longer needed for express trains such as the “Empire Builder” and also had to pull freight trains.