How bicycles balance themselves has been a mystery for ages. Intellectual and curious people have studied how it is possible that you do not fall from a bike while pedaling since the nineteenth century. The bicycle self-stability was explained as the sum of the gyro and caster effects. The gyroscopic effect (gyro effect) of the spinning front wheel is described by the equation of the gyroscope behavior: The torque on the gyroscope applied perpendicular to its axis of rotation and also perpendicular to its angular momentum causes it to rotate about an axis perpendicular to both the torque and the angular momentum. This rotational motion is referred to as precession. And the bike design is to help steer the front wheel into the direction of a lean.
On the other hand, the caster effect is the measure of how far forward or behind the steering axis is to the vertical axis, viewed from the side. Bicycles benefit from the positive caster effect as their steering axis is “in front of” the vertical line.
Surprisingly, scientific studies have demonstrated neither the gyro effect, nor the caster effect are needed to balance bikes. In fact, researchers built a riderless bicycle with two small wheels, each matched with a counter-rotating disk to eliminate the gyro effects, and with the front wheel contact point slightly ahead of the steering axis, giving it a negative caster effect. They launched the bike at more than 5 mph and it balanced itself.
Researchers highlighted the importance of bicycle designs since they “found that almost any self-stable bicycle can be made unstable by misadjusting either the trail, the front-wheel gyro or the front-assembly, center-of-mass position,” the researchers explained in their paper.” (Science, April 15, 2011)
Moreover, they added “conversely, many unstable bicycles can be made stable by appropriately adjusting any one of these three design variables.” Hence, bikes design is important to maintain self-balance.
