This paper first presents original data records of the linear accelerations, along with angular velocities and forward velocity, for a high-speed hands-on bicycle shimmy. These describe the oscillation in terms of duration, magnitude, correlation with forward speed, and related danger for the rider. Then additional experimental data are reported which support the conjecture that the shimmy while riding occurs essentially at the same frequency as the lateral resonance of the head tube when the saddle of a stationary bicycle is laterally constrained.