Richey, Albert S.; Greenough, William C. (1915). Electric Railway Handbook (first ed.). New York: McGraw-Hill Book Company. p. 586 – via Internet Archive. locomotive driving wheel ratio.
books.google.com
Fowler, George L. (1909). Locomotive Dictionary (1909 ed.). New York: The Railroad Age Gazette. p. 37 – via Google Books.
Forney, Matthias N. (1879). Catechism of the Locomotive. New York: The Railroad Gazette. p. 177 – via Google Books.
Rattan, S.S. (2006) [1993]. Theory of Machines (second ed.). New Delhi, India: The McGraw-Hill Publishing Company Ltd. p. 560. ISBN0-07-059120-2 – via Google Books.