Re: Speed on the D&RGW ng lines

It is not possible to properly balance a small drivered (less than 50" locomotive) There isn't enough space on the driver to put enough counterwieght in there. Therefore a 44' drivered locomotive is not going to be properly counterbalanced for "high" speed. The other factor to look at is piston thrust. You can counter balance for the rods or thrust, but not both. Piston thrust makes the engine "hunt" from side to side. Engines built for high speed tend to be counterwieghted for speed and fairly rigid lead truck keeps them pointed straight ahead. This is how the N&W could get thier J's with 70" drivers to run 90mph and the SP and ATSF could get thier 4-8-4's run well over 100mph.

470's were able to run close to 50. I know guys who have been on them at 45 regularly. The scheduled passenger speed on the dual gauge south of Alamosa was about 35mph. 480's and 490's would start to hunt badly at 35 because the piston thrust would overcome the centering device on the pilot truck.