- Overturn mode. Just staying upright is our big problem while learning to ride a bicycle. We all eventually solve it by learning to steer to keep the tires centered under the bike's center of mass.
Wobble is the rapid oscillation at 8–10 cycles per second of the front caster. Wobble typically occurs in the speed range of 35–40 mph, often in step with front wheel rotation and can be excited by front-wheel imbalance or out of round. Riders of some bikes experience a bit of wobble if they take both hands off the bars in this speed range to adjust gloves or face shield. In most cases, the damping effect of putting their hands back on the bars causes this to die away. Wobble damping increases with speed.
Weave is the slower side-to-side swing at 2–3 cycles per second of the rear caster. All motorcycles have a weave threshold, but care is taken in design to place this above the machine's top speed. Despite this, the addition of extra equipment, changes in loading, wear of tires, or loosening of pivots can lower this threshold, making weave possible. Weave is especially dangerous because its lower frequency tempts some riders to think they can "steer" out of it, which often has a reverse effect.
High stability: The disturbance caused by the stick pulse promptly dies away.
Moderate stability: An oscillation is produced, which dies away after X cycles. The smaller X, the higher the stability.
Steady instability: The stick pulse results in a steady oscillation that neither dies away nor increases.
Divergence: The stick pulse produces an oscillation whose amplitude increases without limit. If a divergent oscillation is unchecked, control will be lost.