The Dirtbag Challenge is an annual San Francisco underground chopper building tradition created by Poll Brown. There are very simple rules: build for 30 days, spend under $1000, ride 130 miles around the Bay Area, and no Harleys.* At the end of the ride, there’s a big party with really loud music, really smoky burnouts, and really cheap beer.
It’s SFs little slice of gearhead heaven.
In 2015, Al built a bike for the DBC, and was awarded the “Cleverest” prize.
The bike uses the motor, wheels and about half of the electrical system from a DR650. The frame and suspension were fabricated from scratch, and feature a Hossack front end. The frame is 3” steel tube which completely encircles the engine and creates a 1.75 gallon gas tank. The frame is so tight to the engine, it’s as if it has melted into place. Nothing is hidden or styled, it’s as if a motorcycle has been turned inside out. Despite being hideously uncomfortable due to the tiny seat and very far forward controls, it actually rides and handles better than it looks like it should.
Here’s a video on how the Hossack front end works: https://alanzina.zenfolio.com/p687294330/h5EF40777#h5ef40777
* In 2017, Poll literally doubled down on the format: build for 60 days, spend under $2000, and complete a 3-day, 200+ mile ride, and carry your own camping gear.
Photo of Al with his Dirtbag bike above, taken by Julian Farnam. Photos of Alan Lapp with Poll Brown, and Alan with the trophy were taken by Bob Stokstad.