What role do motorcycle wheel gyroscopes actually play in keeping a moving bike upright?

Answer: They help a little, but tire forces and steering do most of the work.

They do most of the balancing and keep the bike from falling. — This is the attractive myth: spinning wheels look powerful, so it is easy to credit them with most of the job. But a single-track vehicle still needs tire forces, road support, lean, and steering inputs to follow a curve. The gyro story hides the tire-contact and geometry work that actually dominates.

They steer the front wheel for the rider during turns. — Steering is still essential, so this gets the importance of the front wheel almost right. Countersteering starts the lean at speed, and the front wheel then settles toward the angle needed for the turn. Even riderless self-stable bicycles recover by steering into a fall; the wheels do not simply steer for the rider.

They help a little, but tire forces and steering do most of the work. ✓ — Correct. Gyroscopic effects can affect steering feel and help the front wheel return, but models and experiments show they are not the main source of lean or a necessary explanation for single-track stability. The dominant work comes from tire contact, steering geometry, and lean dynamics as the bike follows a curve. Countersteering starts the lean at speed, and the front wheel then settles toward the angle needed for the turn.