In the city where Critical Mass was born, where cyclists stop rush hour traffic dead in its tracks and fixed-gear hipsters ride colonize Ritual like seals on a sun-splashed rock, it's no surprise that we play host to two Bicycle Film Festivals.

Tomorrow night, pump up your tires, put on your helmet and ride on over to the “Vintage Bicycle Film Fest: Fat Tires, Monkeys and Choppers,” an evening of retro films about bike safety, maintenance, history and hijinks held at Oddball Films (275 Capp at 18th). Not just for biking crowd, these flicks from the late '50s to the 1970s should appeal to cycling mavens and camp enthusiasts alike.

Films such as  “Just Like A Car” (a bike safety film that uses stock slapstick footage) and “Bicycles Are Beautiful” (starring Bill Cosby (!) in this McDonald’s-sponsored bike safety and maintenance film) will no doubt cause more laughter than they will prevent collisions. But the 1963 cautionary tale, “One Got Fat”  might scare you straight. In this bizarre/legendary bike safety film 10 (monkey-masked) cyclists ride to the park for a picnic and nine out of 10 don’t come home. The event is $10 and begins at 8:30 p.m.; admission is free if you wear a monkey suit.

This event is merely a prelude, however, for another Bicycle Film Fest, this one a travelling outfit that visits every major US city and will be in SF for the third year in a row. This one runs from July 14 through the 18—the lineup hasn't been announced yet, but we'll let you know when it is.