underfriction

From under- +‎ friction.

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underfriction (uncountable)

1. (chiefly attributive) A system for preventing a rollercoaster train from jumping off the track while in violent motion, using additional wheels under the track.
   • 1928, The Billboard, page 64:

     Altho having 5,000 feet of track, every inc of the route is full of thrill and sensation. Winnwood used the 1922 construction with the safety underfriction and the second coaster was the kids' and adults' "Picnic" type, with around 1,100 feet of track.

   • 1929, Homer Croy, Coney Island, page 208:

     Here knowledge of "banks," pitches, and curves, and acceleration and underfriction in ride-building meant nothing; mystic mazes, fun houses, walk-throughs and Damfino's, which were laugh-getters on a Midway, had no appeal when the same principle was put into a moving picture.

   • 2003, Bret Witter, Carnival Undercover, Plume Books:

     Underfriction allowed coasters to be taller, steeper, and faster than anything previously imagined. The Woodie. Miller built hundreds of underfriction roller coasters out of the only materials available at the time, solid metal […]

   • 2023 August 1, Frank Vizard, Made in New York: 25 Innovators Who Shaped Our World, State University of New York Press, →ISBN:

     ... and underfriction wheels that kept coaster cars locked onto their tracks, a development that fostered higher speeds and allowed cars to turn upside down or bank suddenly.