01-29-2015, 03:27 AM
I understood there have been two scenarios when the SD became available.
One is the most prominent reason of better traction but some railroads had a problem with low quality trackage. They ordered an SD7 or SD9 to better distribute the weight on 6 axle. They did not add additional weight and the tank became often a smaller one. That can be spotted easy. MILW had some of those "light weight" SDs. Look at the tiny tank under the huge engine http://www.rrpicturearchives.net/showPic...?id=155026
One is the most prominent reason of better traction but some railroads had a problem with low quality trackage. They ordered an SD7 or SD9 to better distribute the weight on 6 axle. They did not add additional weight and the tank became often a smaller one. That can be spotted easy. MILW had some of those "light weight" SDs. Look at the tiny tank under the huge engine http://www.rrpicturearchives.net/showPic...?id=155026
Reinhard