to haul longer and heavier trains at relatively low speeds. After
World War I, however, this "drag freight" philosophy began
to change as shippers demanded faster service. As the speed
of freight trains increased, it was found that most freight car
trucks were unequal to the task. Truck springs that cushioned
loaded cars provided a harsh ride when the car was empty, and
vice-versa. In addition, experiments showed that the 39' spac-
ing of rail joints set up harmonic oscillations in trucks at cer-
tain speeds which were so severe that, in extreme cases, the
wheels were actually being lifted up off the track.
24
25
24-25: Two slightly different versions of the ARA 70-ton
truck with 5'8" wheelbase, one by Symington and the
other by American Steel Foundries. The ASF truck had
Barber Lateral Motion devices.
Freight Car Trucks - 10
index
contents
MRH-May 2013
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