Re: Speed debate again - 3 ft. versus 2 ft.

The FRA requires speedometers above 20 mph not ATS.

470's were allowed 45 mph, and did so occasionally did so. They regularly hit 35 on the 3 rail south of Alamosa.

The Valley Line had light rail and was not maintained to run at anything above 20mph.

480-490's were limited to 35mph. Old heads tell me if anyone claimed to run faster than that, they were lying. At 35 the engines began to hunt from side to side terribly.

The deal is you can balance an engine's reciprocating mass (rods) or you can balance the piston thrust, but not both. In the cases where the reciprocating mass was balanced, a pilot truck with greater lateral resistance was used to tame the piston thrust.

The case of the 480-90's a flexible lead truck was needed to negotiate the curves, this pretty much left the piston thrust to do it's thing and at about 35mph it did its thing by making the engine hunt wildly from side to side.

470's could run faster because the lighter wieght of the running gear, and the smaller pistons created less piston thrust. They also carry a greater portion of their weight on the pilot truck, keeping the front planted against piston thrust.