Even cars turning, quoted here as something easy, is deceptively complicated once you really start thinking about what the rubber actually does on the road surface. In the end, both an angular momentum and a centripetal force are generated, but it's very hard to figure out why those things happen from first principles.
Can you explain or provide a link? Thinking about it all seems pretty straightforward to me so I'm curious what I'm missing, what's the complicated part.
Rough approximation is reasonably straightforward, but it quickly gets complicated if you want more precision. At a high level cars want to roll because momentum is resisting a force being applied by the road. But, dig deeper and things get even more complicated.
An uneven amount of weight is distributed to each tire through a turn. Tire temperature, tread, pressure, etc impacts the surface in contact with the road. Even slicks don’t have a uniform pressure across the surface in contact with the road. etc etc.
I'm just a software engineer, not a mechanical engineer, so any explanation would fall short. However, I've been surrounded by world-class Mech E's for decades, so I can remember these conversations being out of my depth!
I've also done urban commutes on bicycle and motorcycle for decades, so I can say given my experience, this is much easier to feel than reason about. You can tell by watching a person ride at licensing whether a person has integrated this feeling or is still reasoning about it.
Hope this helps.
The key to understanding car steering is a concept called "slip angle".
That is, the amount of "misalignment" between the wheel relative to the direction of motion.
Imagine a wheel on a treadmill, with the wheel angled one degree to the right, but held in place so it's kind of slipping slightly. This would have a slip angle of 1 degree.
The fundamental thing is that for a tyre, the lateral force generated by the tire is directly related to the slip angle (also the vertical load and the camber, but these can be removed for a simple model). Slip angle is the main thing.
If you know the relationship between slip angle and lateral force, you can model the movement of a car given the angles of the 4 wheels.
The front and rear wheels have different angles of attack on the vector of the car, so they have slightly different friction vectors.
The result can be oversteer (when the back slide more) or understeer (back slides less).
And it can change depending on road conditions, tire inflation, velocity, acceleration/deceleration. And of course changes radically from vehicle to vehicle.
Covered in depth in the movie Cars "You need to turn left to turn right". :-)
Of course the same thing applies to two wheeled vehicles also - see trail braking.
related content: Would it even be possible to turn left if steering right would be blocked?
"Most People Don't Know How Bikes Work"
https://www.youtube.com/watch?v=9cNmUNHSBac
I've watched literal hours of YouTube videos that explain the physics of steering in the context of motorcycles but none debunk all the misunderstood concepts as clearly as this one. Take my upvote.
(And every time this subject comes up somewhere I am thoroughly amused at all the people who are confidently wrong)
I posted the OP video in a different thread, with this fun fact:
> Another cool thing is how the steering of a bicycle works. You don't really turn the way you want to, you actually turn the other way first to initiate so the bike moves from under you, and you then lean the other way to actually turn. This is why, if you're for instance biking close to a curb and want to get away from it, you really can't and it feels like the curb is "sucking" you closer and closer. Since it "feels" wrong to first turn towards it, but without doing that you actually can't get away from it.
So kinda the same: If a curb or something on your right either blocks you from turning that way, or you "block it in your head" so you refuse to turn the handlebars to the right, you wont be able to actually turn left and get away from whatever is next to you.
I occasionally transport long wood sticks on my bike and when I tie it to the frame so that it sticks in front (3m long, it sticks about 1m in front of the bike) no matter how tight I tie it, it always feels loose. There is this delayed movement of the stick in front that gradually catches up. It's really weird sensation, especially when turning.
Drivers mimic this all the time with their cars. Not for the same physics reason though. They just think that their cars are the size of a dual trailer semi and need a wide turn.
When I was in high school, I rode my bike everywhere. I was mystified by this. I eventually did figure it out by carefully watching what I was doing in a turn. Weird that my body knew it, but my brain didn't!
Except at very slow speeds (walking pace) where I think there's a different mode of action: the bike is no longer self stabilizing and is staying upright more because of your own balance skill. At this point if you turn the bike left it does go left.
...I think. I've been wrong about bike physics before, so I could be again.
Perhaps just me, but this "push left/right" advice messed up my understanding of counter-steer when I was learning and I found myself being unable to turn effectively. I would push the handlebars down or slightly forward and be able to turn but innefectivly.
Far better in my opinion is advice to simply "turn left briefly to go right". As in actually turn the wheel left, then let the bike balance by going right. Moto control explains it effectively: https://www.youtube.com/watch?v=ZLqyN5yy6I8
Depends on your velocity. Push steering works great when riding through a corner at speed. When turning from a stop you need to momentarily turn the opposite direction to initiate the lean.
What's not explained in the text on that video is that braking while leaned over causes a motorbike to steer itself upright.
You can't go around a corner on a bicycle or motorbike at more than about 5mph without counter-steering. You have to tilt the bike into the turn or it will just fall over. You tilt by briefly steering in the opposite direction, which rolls the bike in reaction. This is counter-steering.
Braking while leaned over applies a torque to the steering column towards the side which is closer to the road, i.e. steering into the corner. This torque is due to the width of the front tyre; the contact patch is at an offset to the steering axis. This torque counter-steers the bike upright.
Braking also changes the geometry on most bikes as the forks compress and the bike dives at the front, steepening the steering angle, which makes steering more responsive, so the upright counter-steer is more pronounced.
There's also target fixation. You tend to steer where you look, and if there's an enormous hazard coming at you, you risk steering right into it. Look for the escape routes.
There's also a ground rush panic effect. When something is coming at you really quickly, your instinct is to tense up and brace for impact. When landing a parachute, you're trained to look at the horizon and depend on peripheral vision to feel the ground coming up to meet you, so you flare at the right time. On a bike, it ties in with target fixation; don't look at the fast thing coming at you, look at the escape routes.
I always thought the connection between turning a plane and a bike were somewhat interesting. With a plane, if you rudder left, it causes some right roll. And vice versa. If you roll left, you have to apply left rudder to counteract right raw.
Readit News
An uneven amount of weight is distributed to each tire through a turn. Tire temperature, tread, pressure, etc impacts the surface in contact with the road. Even slicks don’t have a uniform pressure across the surface in contact with the road. etc etc.
https://www.sae.org/news/2018/10/2018-yamaha-niken-chassis-t...
I'm just a software engineer, not a mechanical engineer, so any explanation would fall short. However, I've been surrounded by world-class Mech E's for decades, so I can remember these conversations being out of my depth!
I've also done urban commutes on bicycle and motorcycle for decades, so I can say given my experience, this is much easier to feel than reason about. You can tell by watching a person ride at licensing whether a person has integrated this feeling or is still reasoning about it. Hope this helps.
That is, the amount of "misalignment" between the wheel relative to the direction of motion.
Imagine a wheel on a treadmill, with the wheel angled one degree to the right, but held in place so it's kind of slipping slightly. This would have a slip angle of 1 degree.
The fundamental thing is that for a tyre, the lateral force generated by the tire is directly related to the slip angle (also the vertical load and the camber, but these can be removed for a simple model). Slip angle is the main thing.
If you know the relationship between slip angle and lateral force, you can model the movement of a car given the angles of the 4 wheels.
The result can be oversteer (when the back slide more) or understeer (back slides less).
And it can change depending on road conditions, tire inflation, velocity, acceleration/deceleration. And of course changes radically from vehicle to vehicle.
Covered in depth in the movie Cars "You need to turn left to turn right". :-)
Of course the same thing applies to two wheeled vehicles also - see trail braking.
(And every time this subject comes up somewhere I am thoroughly amused at all the people who are confidently wrong)
> Another cool thing is how the steering of a bicycle works. You don't really turn the way you want to, you actually turn the other way first to initiate so the bike moves from under you, and you then lean the other way to actually turn. This is why, if you're for instance biking close to a curb and want to get away from it, you really can't and it feels like the curb is "sucking" you closer and closer. Since it "feels" wrong to first turn towards it, but without doing that you actually can't get away from it.
So kinda the same: If a curb or something on your right either blocks you from turning that way, or you "block it in your head" so you refuse to turn the handlebars to the right, you wont be able to actually turn left and get away from whatever is next to you.
https://news.ycombinator.com/item?id=35007628
...I think. I've been wrong about bike physics before, so I could be again.
Far better in my opinion is advice to simply "turn left briefly to go right". As in actually turn the wheel left, then let the bike balance by going right. Moto control explains it effectively: https://www.youtube.com/watch?v=ZLqyN5yy6I8
You can't go around a corner on a bicycle or motorbike at more than about 5mph without counter-steering. You have to tilt the bike into the turn or it will just fall over. You tilt by briefly steering in the opposite direction, which rolls the bike in reaction. This is counter-steering.
Braking while leaned over applies a torque to the steering column towards the side which is closer to the road, i.e. steering into the corner. This torque is due to the width of the front tyre; the contact patch is at an offset to the steering axis. This torque counter-steers the bike upright.
Braking also changes the geometry on most bikes as the forks compress and the bike dives at the front, steepening the steering angle, which makes steering more responsive, so the upright counter-steer is more pronounced.
There's also target fixation. You tend to steer where you look, and if there's an enormous hazard coming at you, you risk steering right into it. Look for the escape routes.
There's also a ground rush panic effect. When something is coming at you really quickly, your instinct is to tense up and brace for impact. When landing a parachute, you're trained to look at the horizon and depend on peripheral vision to feel the ground coming up to meet you, so you flare at the right time. On a bike, it ties in with target fixation; don't look at the fast thing coming at you, look at the escape routes.