A riderless bicycle starts tipping left but keeps rolling. What must it do first to save itself?

Answer: Steer into the fall

Lock the front wheel straight — Almost, but a rigidly straight front wheel would leave the bike with little way to bring its support line back under the falling mass. Cornell's summary of the Science work says the test bike straightened after a shove by turning its handlebars toward the fall. The counterintuitive lesson is that balance is not refusal to turn. The useful turn happens before the bike looks saved.

Steer into the fall ✓ — Correct. A self-stable bicycle saves itself by steering into the lean, so its wheels curve back underneath the falling frame. Schwab describes this as a necessary condition for self-stability, and Cornell reports the same behavior in the experimental bike. That is the everyday surprise: a bike can begin its rescue by turning toward the side that looks dangerous.

Lean the frame farther — Not quite. Leaning farther left is the problem unless the wheels also steer left and move back under the bike. Cornell describes the experimental bike straightening after the handlebars turn toward the fall, and Schwab gives the same condition in shorter form. The front wheel has to chase the fall; simply letting the frame lean more does not create that rescue.