From EBBC:
The San Francisco Bike Party rolls out the new year in style with the inaugural ride theme: birthday party. It's a rockin' party for the city! The ride will take a leisurely tour of popular areas in the city with tunes from mobile sound systems. They'll be 3 party/rest stops at well-known locales along the ride. You are welcome to join or leave the ride at any intermediate spot - the route will be posted the week of the ride. Come early to volunteer as a route guide.