underfriction
{{Short description|Roller coaster up-stop wheels that hold cars to the track}}
Image:Roller coaster wheels.jpg
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.{{cite book |last1=Witter |first1=Bret |title=Carnival Undercover |year=2003 |publisher=Plume |isbn=978-0-452-28428-9 |pages=113 |url=https://books.google.com/books?id=1P3fAAAAMAAJ&q=underfriction |language=en}} The design was patented in 1919 by John A. Miller.{{US patent|1319888|Pleasure railway structure}}{{cite book |last1=Cartmell |first1=Robert |title=The Incredible Scream Machine: A History of the Roller Coaster |year=1987 |publisher=Popular Press |isbn=978-0-87972-342-2 |pages=117 |url=https://books.google.com/books?id=Qtyoe7tlkVcC&q=underfriction&pg=PA117 |language=en}}