Another technical reference for this is here:

http://socrates.berkeley.edu/%7Efajans/Teaching/bicycles.htm...

with plots of torque-vs-time and analysis here:

http://socrates.berkeley.edu/~fajans/pub/pdffiles/SteerBikeA...

The author spends most of his time at CERN, but got interested in bike physics for a couple of years.

There's also a sort of "common sense" explanation relying on really basic physics:

Let's say you want to turn left. We know from experience that you will be leaning left when you turn: meaning, your weight is going to be on the left hand side of your wheels. (The common-sense explanation works really well because I'm not going to explain why you need to lean left to steer left, I'm just going to take it as a given.)

The basic-physics question is: if you're starting totally vertical, how the heck do you get your body mass to be on the left hand side of the wheels in the first place?

You can get a little bit of effect, of course, by simply leaning over left: but that leans the bicycle to the right because you can only lean over one way by pushing your bicycle the other way... and when you do this the bicycle briefly opposes you in the way it's leaning before your gravity can win out. That's less good.

So what your brain has actually learned to reflexively do is, to send your wheels going off to the right while your body continues in a straight line, hence your mass is now over the left-hand side of your bicycle and there is no competition. You then steer into the turn and complete it normally.

It seems that they are saying you have to steer right in order to initiate a left lean. But how do they account for steering with no hands?

I can steer pretty well without hands. It seems as if I must be able to initiate the left lean without pushing the handlebars right.

So why couldn't I also do this when not riding without hands?

I can ride pretty well without hands as well. When I heard about counter-steering a long time back I paid closer attention to what I was doing while riding hands-free. Turns out that I was doing a weird little bodily flick motion in to get the wheel pointing to the opposite direction of the turn before I started leaning into the turn.

Pay attention to yourself next time you ride and you might be surprised.

Yep. If you try to just lean right immediately, the bike will just.... fall over, because the wheel stayed straight.

The momentum from the flick your body creates begins to turn the wheel a small amount, and the forward momentum of the bike in combination with the lean keeps the wheel turned right. By contrast, if you flicked the bike/wheel but did not lean, the wheel would simply straighten itself again.

Even for automobiles this stuff is very simple suspension + steering mechanics. Due to how their suspension & steering components are designed, and assuming they are aligned properly, a car will always follow the road. If the road leans + curves, so does their steering.

Yes, I discovered my weird hip tilt when I was using a bad seat. It was then that I realised I barely used my hands to steer at all (sharp turns excepted)

There's a really cool video demonstrating the idea [0]. They took a set of handlebars and welded them to the frame. You'll see that you can affect a motorcycle, but only poorly. On a bicycle, you're much more top heavy and can force the vehicle to capsize far faster. On my motorcycle though? If I lightly increase the throttle it'll go absolutely straight (which is nice if you need to reseat your gloves, but scary if the road starts to veer to the side!)

[0] https://www.youtube.com/watch?v=4PbmXxwKbmA

You can, I think both were described in the theory book for notorcycle license when I glanced through it.

Fun fact: when I read about it I had to test and I had to make sure I wasn't deceiving myself so I put one palm in front of the handle on one side and the other one behind the handle on the other side. That way I could ensure I pushed it the correct way.

It worked exactly as advertised (50cc bike so somewhere below 60km/h).

Much simpler than using slow motion camera etc.

I was under the impression there is a speed at which countersteering becomes apparent and at low speeds it either is minimal or doesn't happen?

It doesn't just happen – you do it. I've never really considered it in the context of a bicycle, but it's the way to turn a motorcycle at any speed above 5mph or so. You'll hear non-riders say that you steer a motorcycle by leaning... Quite the opposite. You steer a motorcycle by steering away from the turn, which causes the bike to fall into the turn. It's the turn that makes you lean, not vice versa. Motorcycles have way too much inertia to affect their path of travel with body weight.

Thinking about it though, I think I did countersteer in order to drop into bowls while riding vert BMX.

That's interesting. In mountain biking it is taught that must lean the bike to turn properly at speed. Some even go a step further and say lean the bike but not your body. I was pondering the physics of why it works the other day but didn't reach a definite conclusion. I guess it makes sense that you can't muscle a heavy motorcycle to lean over, but you could on a much lighter MTB.

Edit: I should mention in mountain biking you are frequently dealing with a low traction environment, which I think has a large impact on the techniques.

You can steer a light motorcycle by leaning, without touching the handlebars.

https://en.wikipedia.org/wiki/Countersteering#Countersteerin...

Sure, and you can steer a heavy slow moving motorcycle by leaning. That's also not what people mean when they say you steer a motorcycle by leaning. Just because you can do it (under some conditions) doesn't mean that's how how steer a motorcycle. Especially since most people are under the impression that you lean into the turn, not out of it.

But yeah, hypothetically lower inertia = more ability to steer with weight, obviously.

Can vouch for this. I was very surprised when, after many years of bicycling, I went to motorcycle school and they taught us this principle. It was insanely cool that it worked.

Hmm, perhaps it's because I learned to cycle later than most people (at 18), but this phenomenon was always very apparent to me. When I first started, whenever I tried to steer I'd always end up going the wrong way.