How do bikes balance

Scientists and engineers have been trying to explain bicycle self-stability since the 19th century. Now, a new analysis says the commonly accepted explanations are at least partly wrong. The accepted view: Bicycles are stable because of the gyroscopic effect of the spinning front wheel or because the front wheel "trails" behind the steering axis, or both. If you try to tilt the axis of a gyroscope in one direction, it will turn in a different direction.

When a bike leans, the gyroscopic effect tends to steer the handlebars in the direction of the lean, bringing the wheels back under the bicycle and helping to keep it upright. Meanwhile, if the front wheel touches the ground behind the steering axis, it will be pulled into alignment with the direction of travel, just as a wheel on a shopping cart turns to follow whichever way you push the cart.

This "trail" gives the force of the ground on the front wheel a lever arm to cause steering in a way that can help restore balance. But at higher speeds, expert riders achieve superior balance performance by employing smaller but more effective body movements and less steering. Regardless of speed, expert riders use smaller and less varying steering inputs and less body movement variation.

We conclude that expert riders are able to use body movements more effectively than novice riders, which results in reducing the demand for both large corrective steering and body movements.

Despite our work and that of others in the field, there is still much to be learned about how humans ride and balance bicycles. Most research, including ours, has been limited to straight line riding, which only makes up a fraction of a typical bicycle ride.

Our work reveals measurable differences between riders of different skill levels. But their meaning is unclear. Are the differences linked to a higher risk of crashing for the novice riders? Or do the differences simply reflect a different style of control that gets fine-tuned through hours and hours of training rides?

If the bike starts to tilt to the left after hitting a bump and succumbing to gravity, the front wheel falls to the left faster than the rest of the bike. As a result, the bike turns left. The amazing part is that turning the front wheel to the left causes the momentum of the bike to snap to the right because of centrifugal force just like you are thrown to the right side of your car when making a quick left turn.

The right lurch of the bike compensates for the initial fall to the left and the bike ends up straight again. The fall becomes self-correcting because of the front-loaded steering geometry. By the way, the centrifugal force is indeed very real in a non-inertial frame, and is not imaginary or fictional.

A riderless bike is not really traveling in a perfectly straight line in a perfectly upright position. It is constantly falling to one side or the other and then lurching back to an upright position under its own momentum. To more effectively demonstrate this concept, which has been known for decades or longer, Kooijman's group built a riderless, gyroscopic-less, caster-less, self-balancing bicycle with front-loaded steering geometry.

There are multiple forces that have an effect on a bike's balance including gravitational force, centrifugal force, and ground reaction forces. To keep things simple, we are going to gloss over ground reaction forces. But in summary, the roll of ground reaction forces is primarily to keep the wheels in place both vertically and laterally on the ground it's because of ground reaction forces that centrifugal force and gravity make a bike lean instead of sliding uncontrollably to the side or falling to the center of the Earth.

There are also effects that assist the rider, including the gyroscopic effect of the wheels and the steering torque effect of rake [1]. But, neither of these effects is directly responsible for keeping the bike upright. And since we're interested on what it is that the rider is doing to keep the bike balanced, we're going to ignore these effects. A rider balances a bike by steering.

More accurately, a rider balances a bike by using steering to constantly generate centrifugal force in a way that counteracts the gravitational force pulling the bike over. If that makes perfect sense to you, you can stop reading - you have graduated. If that only kind of makes sense to you, or if you are totally confused, no worries. We're going to break this down nice an easy. And if you are still with me, good news: pictures are coming up.

Gravity: This one is easy to understand. When you stand a bike up, let go, and it leans and falls to the ground, it's gravity that caused the handlebars to collide so impolitely with the earth.