The physics of bicycles
 

This is from a youtube channel I watch frequently. Pretty interesting that more than a century and we still don't fully understand how a bicycle works.

I 100% understand it. The wheels act as dual gyroscopes.

"reactive torques produced by rapidly spinning objects that resist changes to their axis of rotation"

Come on now. :crash:

Didn't watch the video yet.

There was a really good study about 15 years ago IIRC, I may have links to post, that figured this all out. Collaboration between Delft U in the NL and I think Cornell in the USA IIRC. Gyroscopic forces on the wheels help, as well as front trail (caster), however, the study proved those were not essential for stability, stability being, getting the riderless bike rolling at a running pace and letting go, and the bike self-correcting to stay upright, by steering in the direction of falling.

They used a physical model, and developed a parametric(?) computer simulation to predict behavior. The physical model used tiny inline skate or scooter wheels, very low gyroscopic inertia, and, had the same wheels directly above and in tire contact, to rotate backwards, which they said, cancelled the angular momentum of the bottom wheels, so no stability from that. The front wheel pivot was directly beneath wheel center, so no trail or caster. They called this the Two-Mass-Skate model.

And yet, the bike could be made dynamically (rolling) stable, simply via mass distribution. IIRC(?), the stable configuration was the frame center of gravity being made (with weights) forward of the head tube and high. Note, this parallels experience with front block cargo mounts with load on small-wheel bikes like a 349-wheel Brompton. My 406 wheel bike has no front block, though cargo mass on the front fork rack forward of the steering axis, also improves stability, as it causes steering in the falling direction, as well as adding steered mass to slow down the twitchiness of unladen 406 geometry.

I'll see if I have stored links to the study. Quite interesting.

And here it is. There's videos also:
http://bicycle.tudelft.nl/stablebicycle/

EDIT: Fast forwarding thru video in post #1, ah, they reference the Delft study(s), but don't go into them, treating it like a mystery, which it's not at this point.

More info from my own studies: Longer trail makes steering more stable, however, on smaller wheels like my 20"/406 wheel and smaller, you run into limitations; Because the tire fore and aft of axle center, curves up and away from the ground more quickly than a large tire diameter (because smaller tire radius), and the tire contact patch with the ground is resultingly shorter, that limits the length of trail; If you put the steering axis at the ground forward of the contact patch (picture the front fork on Peter Fonda's chopper in Easy Rider), at lower speeds you get "wheel flop", the steering flopping quickly to left or right, not stable on center. Wheel flop makes the bike front settle to a lower height, and a lower potential energy state, so naturally wants to go there, like a ball on top of a hill and wanting to roll into the valley on left or right. As you increase speed, the trail/caster might cancel out the wheel flop. My own 406 bike has relatively low trail so has little inherent steering stability; Others have 406 bikes that are more stable, I think both due to more trail, and longer wheelbase.

Thank you Doctor!

If it's heavy and/or large radius, it need not be spinning rapidly to have a lot of angular momentum. Large bike wheels with relatively heavy rims, spokes, nipples, and tires and tubes, have plenty of angular momentum, even spinning relatively slow. This is often demonstrated in Physics 1 class when demonstrating Conservation of Angular Momentum. The hub and bearings, being close to the axis of rotation, contribute much less to the total angular momentum.

Linky not working for me... (404 page not found)

As Duragrouch noted, the hypothesis that gyroscopic forces are the major factor in keeping a bike upright was thoroughly debunked some years ago.

Which surprised me a bit when I first read about the studies he cites. But it should have been obvious. After all, any cyclist can easily keep a bike upright indefinitely while moseying along at or below walking speed, where gyroscopic forces are negligible/nonexistent.

Here's a good article on the topic.

Worked for me when I posted, now not. The following link should be a mirror site, different school on the same research team:

http://ruina.tam.cornell.edu/researc...stablebicycle/

I started to, but I need an AI version with an Okie accent.

Did not watch it. I've tried to watch some of that guys other videos but the computer-manipulated voice (and accent) he uses were just too annoying to listen to..

It's not a mystery. It's never been a mystery. Geometry and physics reveal the cosmic truth.

Biology keeps bikes upright, not physics.

Actual bike physics, MIT press
https://cimg2.ibsrv.net/gimg/bikefor...90af0c7293.jpg

another issue not worth solving for the typical cyclist --
a scientific solution for a tire's rolling resistance over a mixed surface gravel ride.

Is there a YouTube version ? 😉

Actually geometry confuses the true fundamental workings of the universe, as does some physics...

The physiques of my bicycles are .....?

Colorful and variable?
https://cimg3.ibsrv.net/gimg/bikefor...fd2fab1bc1.jpg
https://cimg0.ibsrv.net/gimg/bikefor...6b1b0c040a.jpg
https://cimg3.ibsrv.net/gimg/bikefor...e06e595487.jpg

Physics?!, I'm not a Physician!

That's quite a slam-dunk for someone who posts so seldom. Respect.

Pithy, but wrong.

Subtract the biological component from the bicycle, and the bicycle remains self-stable. Physics wins.

we have drone swarm light shows now and people are still posting on the internet "science says bees shouldn't be able to fly"

Except it doesn't work that way.

Indeed. You should have realized that people (not just this guy) looked into the "obvious" explanation. :rolleyes:

We intuitively know how to ride but most don’t know explicitly and often actually believe incorrect ideas.

As usual, Derek does a good job of demonstrating some of the key concepts.


Otto

Scientists have concluded that expert cyclists wobble around less than novices. Intuitively, I've always suspected this, but here's validation from an actual scientific study.

The other way to say it (not mentioned in the article) is that any energy that doesn't help make the bike go forward is wasted effort.

Yup. And the human intuitive counter-steering clowns LOSE. LOL.