Why bicycles work

On a shopping cart, the caster touches the floor behind the steering axis. In this case, the steering axis is the spindle that connects it to the rest of the cart.

This, as you know, lets the caster automatically align itself to the direction of travel. On a bike, the steering axis runs down the fork. If you imagine a line that continues out the end of the slanted fork, it actually hits the ground ahead of where the tire touches the ground. That is, the steering axis is ahead of the contact point, just like on a shopping cart. Jones was so pleased with his discovery that he was still crowing about it 40 years later.

The problem is, he was wrong. While caster trail does determine how easy a bike is to ride, and the gyroscopic effect does help stability, neither is responsible for the self-balancing effect of the bike.

That weight could, in theory, come from cargo on a front rack. So, just how does a bike stay up by itself? In their lab, researchers build all kinds of crazy bike designs to investigate how physics and cycling interact. Who knows? Have something to say about this article? Gears linked by the chain make the machine go faster or make it easier to pedal. Gears are also an example of a simple machine. Gears can make an incredible difference to your speed.

Say the gear ratio on a racing bike is This means a single spin of the pedals will power you about 35 feet down the street. The force used by pedaling enables the gears of a bike to spin the back wheel.

As the back wheel rotates, the tire uses friction to grip the area and move the bike in the desired direction. How much energy are we talking about? Bikes make great use of the most powerful muscles in our body. Brakes on a bicycle work using friction. Although some bikes now have disc brakes, many still use traditional caliper-operated rim brakes with shoes. When you press the brake levers, a pair of rubber shoes clamps onto the metal inner rim of the front and back wheels.

As the brake shoes rub firmly against the wheels, they turn your kinetic energy into heat, which has the effect of slowing you down. The handlebars of a bicycle are actually a type of lever. Longer handlebars provide leverage, which makes it easier to pivot the front wheel of the bike.

The further apart you space your arms, the more air resistance you create. The typical outer parts of the handlebars are for steering, and the inner parts are for gliding. The apparently simple two-wheeled machine uses momentum, force, and friction and converts energy to get riders to their destination.

CBC Radio science columnist Torah Kachur has investigated some of the mysteries, and looked at the latest research on improving bicycle designs. In reality, we know precious little about how the bicycle actually works, beyond the basic mechanics of "pedal turns gear that turns wheel.

But it's the physics that are really fascinating, and somewhat mysterious — the forces that keep a bike going, the variables that make one bike better than the rest, why a riderless bike seems to be able to stay up and ride straight, and what the best design really is.

You'd think with all the interest in high-end bikes, and just how many riders there are, there would be a lot of science in bike design. But that's something of a pervasive myth. Sure, bicycle manufacturers put a lot of effort and energy into designing new carbon fiber frames, different sized wheels or tires with different thicknesses.

But these are typically just educated guesses, as opposed to rigorously tested mathematical principles. Bike design has really just been a "guess and test" model — we know it works because we can ride it, we just don't know why it works. Take the riderless bike, for example. You can push a bike along a path and it almost self-steers. It can recover from wobbles to stay upright. That's ultimately the physics behind why bikes are easy to ride, and yet we know precious little about how that actually works.

A study on this for example concluded, "a simple explanation does not seem possible. And even a video from the YouTube channel Minute Physics concludes, "science currently doesn't know what it is about the special combinations of variables that enables a bike to stay up on its own.