Riding a bicycle is a skill that nearly everyone has learned at some point in their life. However, during the learning process, many are led to believe that the rider is the key to balancing this fun two-wheeled vehicle when in reality, this is not completely true.

The reason is that modern bikes without a rider can balance themselves perfectly fine when launched properly and continue moving as if a person were driving it. Now, let us add to what you have learned in your O-level physics tuition classes and get to the root cause of what keeps bicycles balanced.

The Gyroscopic and Caster Effects

Up until several years ago, physicists believed that gyroscopic effects and caster effects alone are what make a bicycle self-balancing while it is in motion. The gyroscopic effect essentially refers to the phenomena where a spinning wheel has the tendency to remain in alignment with its original direction.

This effect is a direct result of spinning motion or the conservation of angular momentum. It states that when there are no external forces, a system’s total angular momentum retains the same orientation and strength. Hence, a small or weak force has little to no effect on tilting a heavy and fast-spinning wheel away from its original orientation.

Physicists also thought that the spinning wheels of a bike generate sufficient angular momentum to counteract the tilting that happens when the vehicle falls over. And while bike designers fully understood the physics behind their products, they had trouble distilling the large equations down to more digestible concepts like the gyroscopic effect. The experiments conducted in recent years have allowed us to better understand these underlying equations and verify that even if the wheels’ angular momentum gets cancelled out, the bicycle retains its self-balancing effect.

Apart from the gyroscopic effect, many attributed the caster effect to have played a role in a bicycle’s self-balancing nature. It describes the phenomena that occur when there is a difference between the location of a wheel’s contact point with the floor or ground and its steering axis. As this axis moves forward, the contact points fail to keep pace, and the wheels naturally align with the direction of motion.

There are plenty of examples of caster wheels being used in real life, such as those in shopping carts and office chairs. So, whenever you push an office chair in a given direction, its wheels will automatically line up because of the caster effect. Many believed that having a bike wheel’s contact point with the road in front of its steering axis led to a reversal of the caster effect where the vehicle lines up behind the front wheel, which keeps it balanced and upright.

How Bikes Stay Balanced

Although gyroscopic and caster effects may contribute to a bicycle’s self-balancing nature, they are not the main effects, nor are they necessary, as evidenced by recent discoveries. Research by J. D. G. Kooijman and other collaborators has confirmed that front-loaded steering geometry is actually the root cause behind this self-balancing, and it means that the bicycle’s frame and steering shape of its front wheel are constructed in a way the front half of the bike always falls faster than the back.

Hence, if a bike ever starts tilting after going over a bump and succumbs to gravity, you will notice that the front wheel falls much faster compared to the rest of the bike and causes the entire vehicle to bank left. The curious part is that when you turn the front wheel leftward, it will cause the bicycle’s momentum to lurch to the right, a phenomenon caused by centrifugal force. An example is when you get flung to the other side of a moving car whenever you quickly turn left and vice versa.

Returning to the bicycle example, the rightward lurch that takes place counteracts the initial fall to the left and ultimately causes the bike to end up straight again. In other words, the falling motion becomes self-correcting thanks to front-loaded steering geometry. This means that a riderless bicycle is not actually travelling perfectly straight and upright, but rather, it is in a perpetual state of falling to either left or right and going back to the right position under its own momentum.

Conclusion

We learn new things with each passing day, and the facts that we have come to know, such as how balancing on bicycles works, may well be superseded by more concrete evidence and findings as time goes on. As such, it pays to stay up-to-date with the world of physics as we explore not just new frontiers but also challenge established knowledge, the latter being an endeavour that often helps us make progress with the former.

If you are interested in expanding your knowledge in all things physics, then consider signing up for our classes here at Tuition Physics! We are a leading provider of comprehensive and engaging O Level and IP physics tuition in Singapore, backed by many positive testimonials from the countless students we have helped for nearly a decade. For more information about our syllabi and how we can help you achieve your academic goals, feel free to contact us today!