JohnMiller Wheels

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

On roller coaster trains, underfriction, up-lift, or up-stop wheels are a device to keep the train from jumping off the track under intense movement. The design was patented in 1919 by John A. Miller.
Roller Coaster Descriptions
Basic Elements Brake RunLift HillLaunch TrackStation
Advanced Elements Bunny HillHeadchopperInversionsPre-DropTunnel
Lift/Launch Lift Hill (Cable LiftLift ChainElevator LiftFerris Wheel LiftThrill LiftTilt Section)

Powered Launch (Cable LaunchCounterweightFriction WheelsFlywheelHydraulicLIMLSM) Continuously Powered

Technology On-ride cameraOn-ride soundtrackTraincarTrackTransfer TrackUnderfrictionWheel
Other POVQueue LineRollbackTheming