Underfriction

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] This technology-related article is a stub.

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