Sponsored and organized by the Davis Bike Club, the Davis 12/24 Hour Challenge is an ultracycling long-distance bicycling event. Starting and ending in downtown Winters, it consists of a single traversal of a 162.5 mile portion of the Davis Double Century course (referred to as the day loop), follow by repeated traversals of a 18.4 mile course (referred to as the night loop although it is typically reached and started on in daylight). The Challenge offers two events, a 12 hour version and a 24 hour version where participants bicycle as far as they can along the course in this alloted time.

See Bicycling Activities and Clubs for other bike-related events.

A video of one participant's 2007 ride can be viewed at http://www.vimeo.com/882481 (or in low YouTube resolution at http://www.youtube.com/watch?v=Z0tori2_3cE).