to increase the adhesion and improve performance, prr enlarged the sand dome on the s1. it ensured the supply of sand for steam sanding and slightly increased the axle load above the first and second set axle. the s1 was partially de-skirted in 1942 to improve the visibility of the reciprocating parts for the crews and better operation. suspension springs of the pilot truck and trailer truck were fine-tuned to straighten out the overall weight distribution to achieve better performance. railway historian and author alvin f. staufer agrees that she (s1) was oversized and thus unable to visit most roundhouses or handle tight curves, but contends: "she was an excellent steamer and gave trouble-free service."