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Fresh work on the mathematics of bicycles in motion

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Re: Fresh work on the mathematics of bicycles in motion

#61

Post by no_flags »

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…

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.

Re: Fresh work on the mathematics of bicycles in motion

#62

Post by no_flags »

kqr wrote: post #18
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?

Ever thought about why you can't "steer away" from a curb, how it appears to "suck you in" when you try? It's because that first, subconscious turn in the wrong direction takes you into the curb edge.

I've heard this was more of a psychological "target fixation" effect, unless I misunderstand the scenario you describe.

Re: Fresh work on the mathematics of bicycles in motion

#63

Post by mikestew »

upofadown wrote: post #52
dahart wrote: post #47

Earlier quoted context omitted.

> I personally don't consider "countersteer" to be a thing. It sounds like you've never ridden a motorcycle? Most safety courses on motorcycles teach counter-steering, precisely because it is a thing and failure to understand it can compromise your ability to recover from a bad situation. On a motorcycle going fast, you counter-steer continuously. If you make a slow right turn on a freeway, you can turn for 30 second…

>there's only one way to turn without leaning I generated an argument that refutes that statement in the post you are responding to. I am not arguing that the effect does not exist, only that it isn't interesting and is not worthy of a special term to describe it. FWIW I ride motorcycles on a regular basis... I oppose the discussion on countersteering in the regular motorcycle training curriculum because it suggests…

* It would be better just to say that you turn on a motorcycle by changing the angle of the motorcycle from vertical.*

Better than teaching students, "push right, go right. Push left, go left"? Yeah, I'm thinking your way isn't better. Your way, as I read it, just reinforces the idea of "you turn a single track vehicle by leaning". That might have some technical correctness, but it's practically worthless information as far telling a rider what they physically need to do.

Makes for great arguments on the Internet, though, and I'll bet if I cruised over to rec.moto it is still going on some twenty-five, thirty years later after it first started.

Re: Fresh work on the mathematics of bicycles in motion

#64

Post by theOnliest »

davidw wrote: post #54
icc97 wrote: post #48

If nothing else I find it quite fascinating how some bikes are easier to ride without holding the handle bars than others. I can balance much better on my 1998 Specialized Stumpjumper mountain bike (comfortable for minutes without hands) than I can on my 1998 Cannondale R900 racing bike (max 5 seconds without hand). But for my colleague - he finds it much easier to balance his racing bike. As the article suggest - th…

Peter Sagan showing how well some people can ride with no hands: https://streamable.com/2u94 (From today's stage of the Tour de France)

And Ilnur Zakarin (also from today's stage) showing how others aren't as good! Starting at about 2:00 in: http://www.dailymotion.com/video/x4l18sa_flamme-rouge-etape-...

Re: Fresh work on the mathematics of bicycles in motion

#65

Post by HCIdivision17 »

upofadown wrote: post #52
dahart wrote: post #47

Earlier quoted context omitted.

> I personally don't consider "countersteer" to be a thing. It sounds like you've never ridden a motorcycle? Most safety courses on motorcycles teach counter-steering, precisely because it is a thing and failure to understand it can compromise your ability to recover from a bad situation. On a motorcycle going fast, you counter-steer continuously. If you make a slow right turn on a freeway, you can turn for 30 second…

>there's only one way to turn without leaning I generated an argument that refutes that statement in the post you are responding to. I am not arguing that the effect does not exist, only that it isn't interesting and is not worthy of a special term to describe it. FWIW I ride motorcycles on a regular basis... I oppose the discussion on countersteering in the regular motorcycle training curriculum because it suggests…

There's a sort of subtle difference that plays out in how effective the turning is. In countersteering, you don't move the center of mass of the motorcycle-human system; the wheels pull out from under the bike and it naturally turns into the capsizing. Body steering actually moves the center of mass of the system out of the bike's vertical axis. (That is, you're no longer in plane with it.)

Because motorcycles are so massive (at least mine is), body steering is much less effective, but it does help if you want to lean the bike a bit further. That's sort of where the advice to "push down with your legs comes from", since it shifts the bike down as you push yourself up - voila, bike wheels make a deeper u shape, capsizes a bit more, and turns harder. It's a trim knob for turning, kind of how the rear brakes add stability while the front do most of the work.

Like a lot of the points in the MSF course, it's a useful detail to internalize so that when something inevitably dumb/awful happens on the road a poorly trained snap decision doesn't lead to panic (ohgodohgodohgodthebikeisntswervingfastenoug-), but in everyday life you won't be thinking about it directly.

Re: Fresh work on the mathematics of bicycles in motion

#66

Post by handedness »

icc97 wrote: post #48

If nothing else I find it quite fascinating how some bikes are easier to ride without holding the handle bars than others. I can balance much better on my 1998 Specialized Stumpjumper mountain bike (comfortable for minutes without hands) than I can on my 1998 Cannondale R900 racing bike (max 5 seconds without hand). But for my colleague - he finds it much easier to balance his racing bike. As the article suggest - th…

I would guess the frame geometry on your Stumpjumper is likely much more relaxed (specifically the head tube angle) than the Cannondale's.

Re: Fresh work on the mathematics of bicycles in motion

#67

Post by HCIdivision17 »

Someone wrote: post #43
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…

Bikes balance themselves; they don't need a rider to do it for them. Watch https://www.youtube.com/watch?v=oZAc5t2lkvo

I just want to note that this also happens on motorcycles. On a cold winter day my bike dumped me off as I lost traction at a stop light. It started to fall over, bumped its saddle bags, and before the tilt sensor could stall the engine it righted itself in second gear and idled its way through the intersection... with me literally running after it. It hit a curb and eventually stalled upright.

Second most embarassing thing the bike ever did to me.

Re: Fresh work on the mathematics of bicycles in motion

#68

Post by Someone »

nathanielc wrote: post #29
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…

Bike are balanced and symmetric side-to-side. Top to bottom they are not, obviously. The center of mass is above the ground , so a bike that is not moving will fall over to lower its center of mass. But this doesn't happen if the bike is moving. Push a bike without a rider and it will travel for a few feet without falling over, and take longer to fall over if just left standing still.

The surprising thing is that it is way more than "a few feet". Apologies for repeating myself, but watch https://www.youtube.com/watch?v=oZAc5t2lkvo (And that is not on smooth terrain)

And nitpick: typical bicycles aren't symmetric left-right. The chain and gears make them heavier at the right. Most mass is close to the center line, though, so its moment is negligible, especially when ridden by a human.

Re: Fresh work on the mathematics of bicycles in motion

#69

Post by bcook »

Regarding countersteering & bicycles (and motorcycles), I better understood the phenomenon by picturing a bar shoved horizontally through a basketball.

You can steer by either turning the basketball (horizontal plane) or leaning the basketball (vertical plane). In the case of a motorcycle at speed, the bike's effective turning radius is affected more by the lean than by how much the handle-bars are turned. The handle-bars are more about controlling the amount lean.

Re: Fresh work on the mathematics of bicycles in motion

#70

Post by drostie »

mturmon wrote: post #39
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…

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.

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