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Fresh work on the mathematics of bicycles in motion

nature.com

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Re: Fresh work on the mathematics of bicycles in motion

#31

Post by malz »

abakker wrote: post #20

OK - this is probably my ignorance talking, but why is it surprising that bike are balanced? The pedals are basically shoulder width and staggered, which is a very natural position for people to balance in as bipedal creatures? in addition, while the bike is moving, won't the inertia tend to keep things moving in the same direction? This is all coupled by the fact that the rider is actively piloting and adjusting the…

It's surprising to the extent that: balancing on a non-moving bicycle is hard. Riding a unicycle is hard. Riding a bike is easy.

Re: Fresh work on the mathematics of bicycles in motion

#32

Post by mc32 »

Luc wrote: post #14
no_flags wrote: post #9

Avid cyclist, but I have no idea what this is talking about: "...the phenomenon of 'countersteering', whereby the rider can steer to the left only by first briefly torquing the handlebars to the right, allowing the bike to fall into a leftward lean." Am I just doing this subconsciously?

Yes! This PDF explains it very well, with illustrations, on the last page: http://bicycle.tudelft.nl/schwab/Bicycle/DO-07-3-2bicycles.p... "Practically nobody is conscious of the fact that they must steer briefly to the left ion order to make a right-hand turn. But this is not so strange, because the swerve is very small (approximately 3 degrees) and happens very quickly – 0.5 seconds. The wet tire tracks from cyclin…

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?

Re: Fresh work on the mathematics of bicycles in motion

#33

Post by peterwwillis »

Bognar wrote: post #23
SamBam wrote: post #19

Earlier quoted context omitted.

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.

Re: Fresh work on the mathematics of bicycles in motion

#34

Post by ethanbond »

mc32 wrote: post #32
Luc wrote: post #14

Earlier quoted context omitted.

Yes! This PDF explains it very well, with illustrations, on the last page: http://bicycle.tudelft.nl/schwab/Bicycle/DO-07-3-2bicycles.p... "Practically nobody is conscious of the fact that they must steer briefly to the left ion order to make a right-hand turn. But this is not so strange, because the swerve is very small (approximately 3 degrees) and happens very quickly – 0.5 seconds. The wet tire tracks from cyclin…

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.

Re: Fresh work on the mathematics of bicycles in motion

#35

Post by bch »

no_flags wrote: post #9

Avid cyclist, but I have no idea what this is talking about: "...the phenomenon of 'countersteering', whereby the rider can steer to the left only by first briefly torquing the handlebars to the right, allowing the bike to fall into a leftward lean." Am I just doing this subconsciously?

This is really apparent with motorcycles. I haven't personally noticed/tested with a bicycle, though.

Re: Fresh work on the mathematics of bicycles in motion

#36

Post by jessaustin »

sdkjfwiluf wrote: post #3

what was the conclusion ? it's not gyroscopic effects because they still balance with counter-rotating wheels, it's not trail because they can still balance with negative trail. Is it some of each of these effects, if so how much ? What else is involved ?

According to TFA (and to this avid cyclist it makes sense) it is the combination of the two effects you mention and weight distribution. Novel bikes can be constructed that tweak one of these inputs into an unsuitable range and yet still balance, but I really doubt you could mess up all three and still have a bicycle.

Re: Fresh work on the mathematics of bicycles in motion

#37

Post by aninhumer »

Luc wrote: post #14
no_flags wrote: post #9

Avid cyclist, but I have no idea what this is talking about: "...the phenomenon of 'countersteering', whereby the rider can steer to the left only by first briefly torquing the handlebars to the right, allowing the bike to fall into a leftward lean." Am I just doing this subconsciously?

Yes! This PDF explains it very well, with illustrations, on the last page: http://bicycle.tudelft.nl/schwab/Bicycle/DO-07-3-2bicycles.p... "Practically nobody is conscious of the fact that they must steer briefly to the left ion order to make a right-hand turn. But this is not so strange, because the swerve is very small (approximately 3 degrees) and happens very quickly – 0.5 seconds. The wet tire tracks from cyclin…

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.

Re: Fresh work on the mathematics of bicycles in motion

#38

Post by gohrt »

ethanbond wrote: post #34
mc32 wrote: post #32

Earlier quoted context omitted.

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 ha…

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

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

Re: Fresh work on the mathematics of bicycles in motion

#39

Post by mturmon »

Luc wrote: post #14
no_flags wrote: post #9

Avid cyclist, but I have no idea what this is talking about: "...the phenomenon of 'countersteering', whereby the rider can steer to the left only by first briefly torquing the handlebars to the right, allowing the bike to fall into a leftward lean." Am I just doing this subconsciously?

Yes! This PDF explains it very well, with illustrations, on the last page: http://bicycle.tudelft.nl/schwab/Bicycle/DO-07-3-2bicycles.p... "Practically nobody is conscious of the fact that they must steer briefly to the left ion order to make a right-hand turn. But this is not so strange, because the swerve is very small (approximately 3 degrees) and happens very quickly – 0.5 seconds. The wet tire tracks from cyclin…

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.

Re: Fresh work on the mathematics of bicycles in motion

#40

Post by ethanbond »

gohrt wrote: post #38
ethanbond wrote: post #34

Earlier quoted context omitted.

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 ha…

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.

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