The South Australian Railways S class was a class of 4-4-0 steam locomotives operated by the South Australian Railways.

The S class had 6'6" driving wheels, the largest of any Australian locomotive, to give it high speeds on low grades.

[1][2][3] The engines were pushed out of main line service in the 1920s by 600 class locomotives and Brill railcars.

Some locomotives even served in shunting duties despite being unsuitable due to their large wheel diameter.

[3] Media related to South Australian Railways S class at Wikimedia Commons