Bicycle - by Bartosz Ciechanowski
March 28, 2023 12:43 PM   Subscribe

Also, a butt
posted by Going To Maine at 12:54 PM on March 28 [2 favorites]

oh, wow. his piece on mechanical watches (linked in the top of this one) was fascinating. as a recovering bicyclist, I'm really looking forward to spending some time with this one. Thanks, loquacious.
posted by martin q blank at 1:16 PM on March 28 [1 favorite]

This is really interesting. It's fascinating to imagine all that going on for an activity that feels deceptively easy for those who know how to ride a bicycle.
posted by chavenet at 1:31 PM on March 28 [1 favorite]

You can claim a bachelor's of engineering after reading this, right?
posted by Keith Talent at 1:36 PM on March 28 [5 favorites]

Bicycles are really elegant machines. This is a lovely deep-dive. Thanks.
posted by Artful Codger at 2:00 PM on March 28 [1 favorite]

mbrubeck: jinx!
posted by zamboni at 2:18 PM on March 28

Not bad. It handled restoring force/dual track fairly well and did spokes in a "that will do for now" level of detail. The ghost of Jobst Brandt is yelling about something, but I can't make out what.

It did need Mike Burrows and Archibald Sharp in the references, though.
posted by scruss at 2:32 PM on March 28 [3 favorites]

Sooner or later, anything that spins always seems to get around to acting weird.
posted by jamjam at 2:43 PM on March 28 [2 favorites]

Excellent. I had no idea about the way bicycles have to turn right first to turn left, which helps me understand why there's something counter-intuitive about riding a bike to begin with. The way forces are managed with the shape of the frame itself was really interesting, too.
posted by dg at 3:05 PM on March 28 [2 favorites]

I’m afraid to ride my bike now.
posted by slogger at 9:54 PM on March 28 [2 favorites]

I really hope he makes one of these about airplanes... and that it improves my Kerbal spaceplane designs.
posted by kaibutsu at 11:07 PM on March 28

Sooner or later, anything that spins always seems to get around to acting weird.

That's the neat part, everything spins. Everything.

And just wait till you hear about electrons! Just imagine all 7 octillion atoms in your body, each with multiple electrons whizzing around and spinning through space inside you!

Ok it might be just one electron moving very, very fast but that's probably not helping much.

I’m afraid to ride my bike now.

Remember not to think too much about it. If you think too much then bicycles stop working and you fall over.

I'm hoping if I stare at the animations of the wheels and spokes long enough I'll finally be able to true a rim or build a wheel from scratch.
posted by loquacious at 2:57 AM on March 29 [3 favorites]

I once read a heavy book called "Bicycling Science," and the main thing I remember is that, even with a shitload of physics analysis thrown at the problem, we still aren't totally sure why bikes stay upright when you ride them.
posted by Harvey Kilobit at 3:35 AM on March 29 [1 favorite]

They can't. The wing area to body weight ratio is all wrong.

No, wait, that was why bees don't stay upright when you ride them. My bad.
posted by flabdablet at 5:12 AM on March 29 [1 favorite]

Excellent. I had no idea about the way bicycles have to turn right first to turn left, which helps me understand why there's something counter-intuitive about riding a bike to begin with.

Yeah, they teach this in motorcycle safety classes, too.

I can't remember where I first learned this but it was after years/decades of cycling and now it sometimes bothers my brain when I'm riding like I'm suddenly manually breathing, except for steering.
posted by loquacious at 5:23 AM on March 29 [2 favorites]

This is really disturbing! I've ridden literally thousands of miles on my various bikes over the years, and I would swear that I could turn by just dropping my knee into the turn like an axis. Now I must go ride and test this and probably crash.
posted by martin q blank at 7:18 AM on March 29

I don't have my copy of The Bicycle Wheel handy but I do think Ciechanowski's description of how a wheel is loaded and Brandt's description differ subtly; IIRC Brandt describes the hub as hanging from the top of the wheel while Ciechanowski is saying that the spokes below the wheel carry the load through a decrease in tension. I haven't quite wrapped my head around this but maybe the two descriptions aren't incompatible, but rather focusing on different aspects of the system? Regardless, this is excellent and is the best visual description of wheel building I've ever seen.

Re: countersteering, my experience is that it's much more obvious at high speeds or on larger bikes (like cargo bikes). Below 15mph on a road bike I've found it difficult to discern, but pay attention when you're on a descent. Consciously countersteering is really fun.

Ciechanowski is an absolute gem.
posted by kdar at 7:25 AM on March 29 [1 favorite]

This looks great and I wish I had time to read it. My next physics read/listen is going to be Feynman's lecture on the principle of least action.
posted by neuron at 8:44 AM on March 29

I'm hoping if I stare at the animations of the wheels and spokes long enough I'll finally be able to true a rim or build a wheel from scratch.

loquacious, you really only need to stare at one thing: the Professional Guide to Wheel Building, 7th Edition.

It's really a lot simpler than it seems once you grok what's involved. On a good day you'll breeze through it. On another good day, you can spec your first wheel. Two more good days and you'll lace, tension and stress-relieve it.
posted by tigrrrlily at 9:01 AM on March 29 [1 favorite]

I would swear that I could turn by just dropping my knee into the turn like an axis.

Steering a bike is done by altering the centre of mass of the whole rider+bike assembly so as to put it off the straight line that joins the two ground contact points.

Doing that adds a nonzero sideways component to the assembly's weight vector i.e. in a direction at right angles to that of its forward motion.

A constant force that's continuously applied at right angles to a body's direction of motion causes that body to accelerate, because that's what any applied force will always do. But because it is at right angles to the direction of motion it has no component in the direction of motion, which means that the acceleration doesn't affect the body's speed. Rather, it manifests as a constant rate of change in the direction of the body's motion. A constant rate of change of direction makes the body follow a circular path, with the body's direction of motion always tangential to the circle and the sideways acceleration inward along the circle's radius.

That's centripetal (centre-seeking) acceleration, and the force that causes it is centripetal force. It's the same kind of acceleration that the force of string tension applies to any rock you tie string to in order to whirl it round your head.

The countervailing force that the rock applies to the string is centrifugal (centre-fleeing, fugal as in fugitive) force. Centrifugal force is a real force, despite generations of careless pedants claiming otherwise; but it acts on whatever is constraining a body to move in a circle, not on the body itself. In the context of rock and string, the centripetal force acts on the rock, pulling it inward to follow the whirled circle; the centrifugal force acts on the string, keeping it stretched in tension and trying to pull it outward from the centre. In the context of a turning bike, the centripetal force acts inward on the tyres and the centrifugal force acts outward on the ground.

Centripetal and centrifugal forces act at the same points (where the string holds the rock, or where the rubber meets the road) but always in opposite directions.

So let's get specific now, and think about what happens when you want to steer a bike to the left.

You want to end up with your centre of mass off-axis to the left, by just enough for your weight to contribute exactly the centripetal force you need to make the bike track left as sharply as you want it to, and there are a couple of approaches to getting this done.

One way is to shift your body over to the left a bit by changing its shape. Getting that shift motion started requires having the bike apply a brief net leftward force to your body, which your body arranges for by applying a brief net rightward force to the bike. So the very first thing that the bike is going to do, as your weight transfer process just begins to happen, is accelerate rightwards - that is, it will track some way in the opposite direction to that in which your weight transfer will soon make it settle into tracking. That initial tracking change, which doesn't last for very long - not even as long as it takes you to finish shifting your weight - is countersteer.

Another way is deliberate temporary interference with the handlebar-based balance feedback loop that normally keeps your centre of mass's track aligned with that of the wheels. If you shove the handlebars to the right just a little then the front wheel will track to the right a little, and the bike will start coming out from underneath you to the right. But before that process can get out of control you stop fucking with the handlebars and hand them back to your automatic stabilizer, which then starts maintaining your body's new relationship to the frame i.e. hanging off to the left of it in a nicely controlled centripetal force mediated steady left turn. But that initial come-unstuck-to-the-right manoeuvre is also countersteer.

Most riders unconsciously and instinctively use an integrated combination of all of those movements, and consciously trying to tease them all apart while riding is probably going to hurt that smoothness. If you're going to play with your riding style For Science, do it where there's not much around to bump into.

In general, concentrating on shifting your body over the frame while letting your hands and the handlebars just keep doing whatever they do will give you very smooth and well controlled turn initiation. It's the right thing to do on the track, where smoothness translates to speed, and there is time to plan and practice your racing line, and the best lines are the ones with as little steering input as possible.

Deliberate temporary destabilization by initiating turns with the handlebars is going to throw you around more, and make the bike change more quickly from tracking straight to tracking curved, with the centripetal force that the road applies to the tyres going from zero to steero much more quickly. Done with skill, though, the maximum contact patch force needn't ever peak higher than it has to anyway during the steady phase of the turn. Which means that if you deliberately practice initiating turns via handlebars-based countersteer, you gain skills that can keep you safer when you need to respond fast to unexpected obstacles on the road.
posted by flabdablet at 9:20 AM on March 29

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