Since 1992, thousands of cyclists have gathered on the last Friday of every month to show off their bike pride by getting in the way of auto traffic on city streets in the Critical Mass demonstration rides.

As part of KALW’s special bike coverage, we bring you the history of the most prominent bike protest institution, as remembered, in a lovely audio montage of reminiscences from the movement’s three founders.

As they explain, biking in San Francisco was rough and tumble in the early 1990s: “Drivers used to throw things at you and tell you to ride on the sidewalk.” Anger was daily and universal, they tell KALW, ”a lot of obscenities … people would pound on their horn.”

So a mass ride to reclaim the streets for cyclists one night a month was planned. ”The beginning of it was essentially a bunch of people who had been talking about the idea of riding together as a political statement as an act of reclaiming the city,” explained the third founder.

About 50 people came from the first one, and within a year 1,000 riders were showing up for the monthly ride, originally called “the commute clot”.

That’s not such a catchy name for spreading a movement, so the founders tell KALW how the term critical mass came to be. They adopted it from a documentary by Ted White, Return of the Scortcher, where cyclists at a Chinese intersection documented in the film have to wait until there is a critical mass of bikes in order to break into the intersection and stop oncoming car traffic to cross as group, in safety.

Today, the gatherings take place in hundreds of cities, drawing thousands of riders in the biggest cities and follow no set route, blocking car traffic completely on avenues as the bike horde meanders through urban centers. Often times, the un-permitted rides provoke police responses that lead to arrests.

Listen to the full story of the start of critical mass, and how the unplanned routes came to be the norm.