A roller coaster wheel assembly. The underfriction wheels are on the bottom. The three sets of wheels clamp onto the track.

On a roller coaster train, the underfriction, up-lift, or up-stop wheels are a device to keep the train from jumping off the track under intense movement.[1] The design was patented in 1919 by John A. Miller.[2][3]


  1. ^ Witter, Bret (2003). Carnival Undercover. Plume. p. 113. ISBN 978-0-452-28428-9.
  2. ^ Pleasure railway structure
  3. ^ Cartmell, Robert (1987). The Incredible Scream Machine: A History of the Roller Coaster. Popular Press. p. 117. ISBN 978-0-87972-342-2.
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