Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Fresh work on the mathematics of bicycles in motion

nature.com

Post reply on HN
Print view View original

11–20 of 100 posts

Re: Fresh work on the mathematics of bicycles in motion

#11

Post by artimaeis »

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?

I've never noticed this on bicycles, but I also haven't ridden anything but a stationary in 5+ years now! But this is very noticeable in motorcycles.

Most riders don't really think about the torque they're applying to the handlebars, but when you lean into a turn you're definitely applying that torque to the handlebars. You're kind of putting the side of the wheel to the ground in the process, and the only way to put the side you want to turn to towards the ground is to torque the handlebars in the opposite direction.

Re: Fresh work on the mathematics of bicycles in motion

#12

Post by pcmaffey »

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?

Its crazy seeing motorcycle racers countersteer to get a deep, knee-on-the-ground lean into a turn, with the wheel and handlebars turned the opposite direction.

For cycling, I can only explain this passage by saying I lean a little left first, possibly providing that right torque, which then enables the handlebars to turn fully left into the turn.

But I have no idea what I'm talking about.

Re: Fresh work on the mathematics of bicycles in motion

#13

Post by recursive »

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?

Probably. If you care enough, and have the facilities, you can take a slo-mo video of yourself taking an abrupt and sharp turn. You will find that counter-intuitively, your bars first turn the opposite direction. In any experienced cyclist, this just becomes an innate instinct.

Re: Fresh work on the mathematics of bicycles in motion

#14

Post by Luc »

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 cycling experiments reveal that we all do this. Apparently we learn this unconsciously when we learn to ride a bike."

Re: Fresh work on the mathematics of bicycles in motion

#15

Post by rconti »

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, it's subconscious (and/or you are initiating the turn by leaning into it, which causes the bicycle to countersteer FOR you).

The way I describe it is that the wheels MUST be underneath the force exerted by the center of mass. In straight-line riding, this means your wheels are under you. In a corner, your mass is to the "inside" of the corner, but the centripetal force added to gravity's downward force ends up pushing down to where the wheels are.

So you need to steer a bicycle so that the wheels are always under this center of mass force (I'm sure there's a word for it).

Hence, if you were to turn the wheels in the direction you wanted to turn, you'd fall over, off the bike, to the outside of your intended turn.

Therefore, to initiate a turn, you have to steer the wheels out from under the bike (the "wrong" way) to initiate your mass's 'fall' into the corner. Then you steer the wheels back under you to balance the fall.

Re: Fresh work on the mathematics of bicycles in motion

#16

Post by HCIdivision17 »

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?

It's wildly unintuitive, so don't feel bad. When I was first learning to ride a motorcycle with the MSF, I damn neared dumped the practice bike a few times trying to manhandle it. You'll really quickly internalize push-left-go-left. And it turns out to work great on regular bikes, too. (But it's terrifyingly more responsive - I actually can't relax pedaling a bicycle because of the fear of how easy it is to flip the things and capsize them from countersteering.)

EDIT: There's a neat heuristic that was brought up in the course: the center of mass of the bike is above the bottom of the wheels, and a turning bike must lean into the turn (weird road geometries excepted), therefore to turn the stuff under the center of mass must counter the top leaning in. Thus to go left, you push left, causing the front wheel to pull out from under the bike right-wards, which starts to capsize the bike leftwards! Like I said before, a bicycle reacts really really hard to this, but a hefty motorcyle has a far lower center of mass and leans into it more gracefully.

Re: Fresh work on the mathematics of bicycles in motion

#17

Post by ranko »

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, you're doing it subconsciously. Countersteering is only possible on two-wheeled vehicles, which means that tricycles handle very differently to bikes, and that learning to ride with stabilisers (training wheels) can be counterproductive.

Re: Fresh work on the mathematics of bicycles in motion

#18

Post by kqr »

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.

Re: Fresh work on the mathematics of bicycles in motion

#19

Post by SamBam »

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…

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?

Re: Fresh work on the mathematics of bicycles in motion

#20

Post by abakker »

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 to keep it under control at all times. The bike seems like it would balance to me because the control mechanisms are designed to keep things balanced easily.

Post reply on HN