Living rooms became bike shops among dusty cottages in the heart of Marin County, as a group of countercultural road cyclists began riding their 1940s balloon-tire ‘klunker’ bikes on dirt. They ended up inventing the world’s most popular bicycle - the mountain bike.

A catalyst for this mashup of invention and fun was the Appetite Seminar. Intended to build up an appetite on Thanksgiving Day, it started with a handful of pioneers hiking and riding the grueling Pine Mountain Loop in 1975. Since then, the ride has been repeated every year, making it the world’s longest running mountain bike event. It now attracts hundreds of riders every year from across the world.

The Appetite Seminar tested your endurance. But with the ride ending on a treacherous descent, soon enough they wanted to know who was fastest down the hill. This led to the world’s first downhill bike race, the Repack series, and the evolution from clunkers to custom-designed downhill machines.

This film explores the origins of mountain biking, and how a few pioneers just having fun changed the world.