The stability of a bicycle depends on its speed and its weight. Stability has both advantages and disadvantages. The explanation is split into the following four points:
The faster one cycles, the easier the bicycle stays upright by itself. Cycling at an average speed over a straight road is very well possible with minimal steering impulses, and often even without hands. At a low speed, a bicycle will only stay upright as a result of a correct combination of steering and body movements.
A stationary bicycle is completely unstable, and when mounted by a rider, it can only stay upright thanks to the balancing skills of the rider. Balancing is a delicate combination of steering and body movements. During balancing, the rider keeps the combined center of mass of rider and bicycle above the tipping point. (The tipping point is straight above the line that connects the two contact points of the tires with the road surface.) If the center of mass lies to the left of the tipping point, you fall to the left, and if it lies to the right, you fall to the right.
Both a heavy and light bicycle fall over when they are stationary. However, the difference between a heavy and light bicycle is that steering impulses and body weight displacements of the rider (the input) are less effective on a heavy than on a light bicycle. This goes in both ways:
- For a bicycle in a stable position (e.g., upright at high speed), rider input is less distorting as the bicycle is heavier.
- For a bicycle in an unstable position (e.g., tipped over at low speed), corrective rider input is less effective as the bicycle is heavier.
The increase in stability with speed is a nice property that we can use to our advantage. For example, some cyclists have difficulties with riding off. Instead of balancing the bicycle at low speed, these cyclists can better practice on speeding up as fast as possible (i.e., accelerating).
For some cyclists, also stopping is a difficult action, and again it is useful to know that stability depends on speed. Because of this property, it is always a bad choice to stop in turn. In a turn, the bicycle always leans to the inside, and this position becomes unstable when slowing down. Save stopping therefore starts with selecting a straight line to the stopping place, such that there is no need for braking in a turn.
The reverse side of the increase in stability with speed is that the bicycle also becomes less viable with speed. Concretely, the higher the speed and the heavier the bicycle, the stronger the steering impulses that are required to make a bicycle change direction. Cyclist that switch from a regular an e-bike often experience problems with this; an e-bike is faster and heavier than a regular bicycle.