Basically, they took a bike with two small wheels and built in mechanisms that canceled out the caster and gyro effects. Launched at a speed of 5 mph, the bike stayed upright. When it leaned to one side, the bike righted itself. Just like any old bike would. “It’s all about how bicycle leaning automatically causes steering, which can bring the wheels back under a falling bike,” explains Andy Ruina, professor of mechanics at Cornell and a co-author of the Science paper.
So, the key to making a bike unstable is screwing around with a bike’s ability to steer itself. Or by misadjusting the “trail, the front-wheel gyro or the front-assembly, center-of-mass position,” the paper explains in more technical-speak. The researchers expect their work might be used to innovate bicycle design in ways thought impossible before: “The evolutionary process that has led to common present bicycle designs might not yet have explored potentially useful regions in design space.”