Sure, the basic mechanics are understood — but questions remain about the physics of bikes
While many people know how to ride a bike, we know surprisingly little about the science of how cycling actually works, says CBC columnist Torah Kachur. (AFP/Getty Images)
"It's as simple as riding a bicycle" is a common expression. But the science of two wheels staying upright is anything but simple and we still know little about the intricacies of how cycling actually works.
What mysteries still remain about bikes?
A better question might be, "What DO we actually understand about bikes?"
We know little about how the bicycle works, beyond the basic mechanics of "a pedal turns a gear that turns a wheel." It's the physics that are really fascinating and the forces that keep a bike going are somewhat mysterious. 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.
Although the basic mechanics of bicycles are well understood, the physics behind cycling remain somewhat mysterious. (Image | Wild Atlantic Cycling)
Bike design has been a "guess and test" model — we know how it works because we can ride it, but we don't really know how it works.
Quantum physicist Michael Brooks summed it up nicely in a 2013 article in the New Statesman:
“Forget mysterious dark matter and the inexplicable accelerating expansion of the universe; the bicycle represents a far more embarrassing hole in the accomplishments of physics.
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You can push a bike along a path and it almost self-steers. It can recover from wobbles to stay upright. It's ultimately the physics that comes into play as to why bikes are so easy to ride but we know little about how it actually works. A 2007 study on this even confirms, "that a simple explanation does not seem possible."
Want a bike physics lesson?
Illustration from the Proceedings of the Royal Society of the angled steering axis of a bicycle. (from the Proceedings of the Royal Society)
First, we know the reason a bike will continue on its path isn't just because of the force of momentum pushing it there. We know that because if you lock a bicycle's handlebars so that they can't turn, then the bike falls over, regardless of how fast it's moving. So part of this riderless bike phenomenon has to do with its self-steering properties.
Second, a key property of the bike’s stability is its handlebar angle. If you look at a bike, you see the fork — the part that splits and connects to your tire at the front — is angled.
That angle means the steering axis — the line that the bike is steering on — is ahead of where the tire actually touches the ground. The effect of this is simple — all of us have leaned a bike against a wall, only to have the tire tilt and swing out to the side, resulting in the bike sliding down the wall. That's because the steering axis and the contact point are at different places, so the front tire moves towards the steering axis, which helps the bike self-steer, and makes the bicycle stable when a rider is on it. If the fork was at a 90-degree angle to the ground and sticking straight up to the handlebars, the bike would basically not be steerable.
What we still don't know is how these forces, as well as the gyroscopic effect of the tires turning, interact with one another. We don't know what the major driver of bike stability is, and how the interacting forces can be maximized to create a bike that is more stable and easier to steer.
Okay, so what about bike design?
Bike design hasn't really improved in decades, says Jim Papadopoulos. He's a bicycle enthusiast and a mechanical engineer at Northeastern University, whose research on bike science was recently featured in Nature. Bike designers have focused on crafting lighter bikes, with carbon fiber frames. A bike that weighs three pounds or less might sound impressive until you think that you are about to load that frame up with a rider who might weigh 150 pounds or more. Three pounds lost on the frame simply means you have gained a two percent efficiency, which for most of us would account for a few fractions of a minute shorter time for our usual rides. It might make a difference to the best riders in the world but not so much to a casual bike rider. A well-designed bike also depends on the rider who's on top of it. The best shock absorber is the bent arms of the rider, and the best generator of a forward force is the power of the legs behind it.
The main takeaway is that while we can credit the bike for many things, the real machine is the athlete driving it forward.
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we have a nifty guide if you love biking throughout Brooklyn
