Hacker News Reader

Comment by whycombinetor | Hacker News Reader

The author lost all credibility when he said I have to countersteer to turn my bike. The author is a "professional engineer and consultant, specializing in feedback systems and motors" too. There are >50 million cyclists in the US who would presumably immediately recognize this as a false statement and he didn't ask a single one of them to proofread.

Edit since some people are confused by this apparently: You can steer your bike away from the edge of a cliff by leaning to initiate the turn instead of countersteering. This makes the author's advice of "Don’t ride your bicycle on the edge of a cliff" much less critical.

View on HN

In the interest of defending my credibility, consider the challenge of explaining some concept to an audience using concrete examples, when any example has subtle associated details and exceptions that, while fun to explore on their own, do not further the goal of explaining the original concept.

If you'd prefer, I can explain the concept of the right-half-plane zero using only abstract systems described by transfer functions. But I suspect that will be less effective from an education standpoint.

I maintain that countersteering a bicycle is an excellent example of a RHP0, and it's no coincidence that a translating inverted pendulum also has an RHP0 in its control solution.

I also am one of those cyclists and, at least prior to the pandemic, commuted by bicycle every day.

One can always test the hypothesis via an experiment:

https://youtu.be/9cNmUNHSBac

Heh was about to reply with the same video. It’s really counterintuitive even for people who ride a lot

It's counterintuitive to cyclists because we don't countersteer. We lean instead, generally subconsciously. If we didn't lean, it's true that we'd have to countersteer... but nobody rides that way, making it a flawed analogy at best.

I’m not good downhill mtb rider but my understanding it’s really common technique there. Even on road i do that not to take a spill in sharp-ish downhill turn going at speed

You always countersteer; you're just not doing it consciously. Because of that, you're doing it very slightly. Because you're doing it slightly, you enter into turns slowly. You're not able to take sharp corners at a decent speed.

You cannot lean without countersteering first; the lean happens because you induced a fall in the desired direction, through a tiny countersteering move. With the tiny, subconscious counter-steers, you induce only small tilts. I suspect it takes multiple small counter-steering maneuvers to "build up" a decent tilt for a sharp turn, which takes time.

Once I learned to deliberately countersteer, I then started doing it all the time. I hardly take any turn (big or small) on a bicycle without pushing forward the handle-bar on that side.

If you don't make deliberate countersteering your main steering method, so that it becomes second nature, you will not be able to count on yourself to use it in an emergency.

Maybe you countersteer. I don't. I checked by riding through a puddle, turning right, and then checking the resulting trail left by the tires. No overshoot whatsoever.

Your interpretation of the trail must have missed something. We know that all turning of a bike is via countersteering. You wouldn't be able to turn right on a bike whose steering is locked out from turning left. (See video upthread.)

You can ride a bicycle that is locked out from steering at all. (You can ride one-footed on anti-rocker (2 wheel) inline skates, with some practice).

Indeed. I like this clip where they show bike steering to the left, without its front wheel ever going to the right side of its original path, by only leaning and no countersteering. https://youtu.be/9cNmUNHSBac?t=445

That's with no rider on the bike. Earlier in the video when he attempts to turn with the device that prevents countersteering, he falls off every time. It seems unlikely that 50M cyclists could easily do this but he could not.

The bicycle and riding style used in the video do not provide a good illustration, I have no idea what he was trying to do as he crashed repeatedly, and he did not seem (or the frame prevented him) to use the ability of his body to lean the bike into the turn, riding naively (which didn't prevent them from talking down as if there is a clear consensus in the field of bicycle dynamics).

At low speeds on e.g. a light MTB stop pedaling, lift your butt off the saddle, lean bike far into desired side balancing your body and handlebars to keep going straight. You have most of what's needed to turn. You may countersteer but your line does not veer into the direction of countersteer, counter to illustrations.

Riding edge of a cliff is not a great idea anyway because balancing a bicycle tends to require countless small adjustments even due to pedaling alone.

> The bicycle and riding style used in the video do not provide a good illustration

It's good enough if you already understand it and know what to look for; just not the best for convincing someone who doesn't believe the physics.

You don't just believe the physics. If there is consensus in physics that says you cannot turn a bicycle without measurably turning the opposite way first, feel free to link. It's a ridiculous claim that assumes certain speeds, bicycle type and riding style. I've seen a guy ride a narrow rocky ridge, even jumping from stone to stone where needed (without stepping off the bicycle), was he violating laws of physics or is the world more complex than simplified models of it? Either way, it is just bikeshedding.

Now just imagine the possibilities with a rider on the bike. Being able to dynamically shift weight to either the left or right side of the bike at will! You can even do turns while riding with no hands.

When you shift your weight to the left, the bicycle tilts right to keep the center of gravity above the track line.

If this were the case, you wouldn't be able to turn while riding with no hands. Yet reality has us out here riding bikes with no hands making turns. https://youtu.be/_SWdCutqSWQ?t=73

That is false, because you can induce a motion of the steering column without using your hands. If you shift your center of gravity around without your hands on the bars, the steering column will do things on its own and you can learn to predict and control that. Not just simply 0shifting the center of gravity in the seat; you can do things if you seize the top bar between your knees.

A steering column which somehow turns right without your hands will induce a countersteer to the left the same way as if you had used your hands.

> That's with no rider on the bike.

That's irrelevant; bicycles countersteer to keep stable, without a rider present (above a certain speed).

If the riderless experiment were repeated with a bike whose steering is locked out, it would fall down rather quick.

The video shows the exact opposite of your claim. The bicycle is given an initial push by the experimenter. Its steering is initially pointing a bit to the left. Because of this, it begins falling to the right, and recovers by steering in that direction, away from the guardrail.

The bike seems to be initially leaning to the left, because it was induced into motion that way by the experimenter. Yet in spite of this, it recovers by tilting to the right.

Looks to me like 1. The bike is initially rolling straight with no handlebar angle, and then starts falling over to the left. 2. Due to the mechanic explained in the video, this causes the handlebar to turn left.

If there was a human on that bike wanting to turn, here they would continue leaning, turning, and pedaling in the correct amounts.

But because there's no human to keep their weight leaned to the left, then 3. The left turn of the handlebars causes the road contact points to move to the left of the center of gravity, so that 4. It starts turning right.

I'm curious how you're so confident about this. I think if you ask most people (even most cyclists) what happens when you turn the handlebars to the right, they'd say you turn to the right. I cycle almost every day and I thought this for a long time. Have you actually tried it? When I tried it, I found that it forces me into a left turn.

Have you tried leaning to the left while biking in a straight line? It results in you turning left without your front wheel ever having gone to the right (i.e., turning without countersteer).

> Have you tried leaning to the left while biking in a straight line?

That is impossible. If you lean your body left while biking in a straight line, the bike will lean right to keep your center of gravity above the track.

For bike and body to be leaning left, the bike must already be in a turn. Or else, it must be in the middle of a fall.

Two-track vehicles always begin a turn with a countersteering move which induces a fall in the opposite direction. Then the steering immediately switches in the falling direction, to convert the fall into a turn.

(In the absence of wind anyway. A left turn could plausibly start without a countersteer if a gust of wind blows over the bike into a left lean; the subsequent left steer and turn will supply the compensating acceleration to prevent a fall.)

A bicycle is always countersteering. A bicycle whose steering column is locked out, prevented from turning, cannot be ridden. It will fall over.

A bicycle doesn't require a rider in order to maintain balance, either. Above a certain speed, a bicycle can correct itself. This is due to countersteering. Whenever the bicycle accidentally steers slightly to the right, it begins to fall to the left, and this provokes a left steer which prevents a fall.

A rider who doesn't understand countersteering nevertheless intuitively "bootstraps" the turn out of these small wobbles, gradually increasing the tilt and and degree of turn, through a sequence of small counter-steering maneuvers.

Reply on news.ycombinator.com