Underfriction

File:Roller coaster wheels.jpg

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.<ref>Template:Cite book</ref> The design was patented in 1919 by John A. Miller.<ref>{{#if:1319888 |[{{#ifeq:|uspto|http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=%7Chttps://patents.google.com/patent/US}}{{#iferror:{{#expr:1319888 }}|1319888}} Pleasure railway structure] |{{US patent|123456|link text}}}}</ref><ref>Template:Cite book</ref>

References

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