[HN Gopher] The Counterintuitive Physics of Turning a Bike (2015...
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The Counterintuitive Physics of Turning a Bike (2015) [video]
Author : thunderbong
Score : 32 points
Date : 2023-03-03 13:59 UTC (2 days ago)
(HTM) web link (www.youtube.com)
(TXT) w3m dump (www.youtube.com)
| dvh wrote:
| 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.
| toxik wrote:
| Bike-based jousting? Interesting concept!
| hanszarkov wrote:
| Part of the Motorcycle Safey Foundation (MSF) curriculum since at
| least the 1990s: "push left go left, push right go right"
| billyt555 wrote:
| Also a core part of Keith Code's teaching since I think the
| 70s. Highly recommend his school for any motorcycle rider.
| https://superbikeschool.com/the-curriculum/
| bobogei81123 wrote:
| And not understanding that can have fatal consequences:
| https://youtu.be/VVE79XT8-Mg
| barrkel wrote:
| 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 steering in the opposite direction, which rolls the
| bike in reaction, aka 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 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.
| codeflo wrote:
| 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.
| crazygringo wrote:
| 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.
| Retric wrote:
| 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.
| cjsplat wrote:
| 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.
| [deleted]
| 11235813213455 wrote:
| you can also move your body to create the angle and then slightly
| turn to the desired direction
| mulmen wrote:
| A motorcycle is too heavy to do this so you you counter-steer
| to overcome the gyroscopic stability and change the angle of
| the bike. Essentially you are attempting to _destabilize_ the
| bike, in a controlled manner.
|
| The same physics apply to a bicycle.
| andrewflnr wrote:
| FWIW I think that's only _mostly_ true. I 'm told there are
| some situations where you really do just shove the bike over
| into a lean. Of course even if that's true, it's very much a
| case of (as I like to put it) the exception that highlights
| the common case. :)
| engineer_22 wrote:
| Swerving around an obstacle in the road you might do this
| NikolaNovak wrote:
| Yes; on bicycle it is certainly possible to ride and maneuver
| at speed without touching the handlebar, weight shift only. (Or
| at least it was possible 25 years ago when I was more nimble
| :-)
| lisper wrote:
| There is a trick to this: grasp the seat firmly with your
| thighs and think about trying to turn the bike by pushing
| sideways on the seat with the insides of your thighs.
| sethammons wrote:
| It is really counter intuitive. Next time you are riding down a
| hill, dont lean or anything, and slightly push the left
| handlebar forward. Without leaning, you will turn left.
| askvictor wrote:
| This is also the basis of an emergency swerve on a motorbike
| - if you need to turn left suddenly you push the left
| handlebar hard.
| Zak wrote:
| Countersteering is the basis of _all_ steering on a
| motorbike.
| askvictor wrote:
| And a bicycle, but the point is you don't notice it when
| you do it (except an emergency swerve)
| ithkuil wrote:
| What happens if you have a sidecar?
| NikolaNovak wrote:
| If it's attached firmly, you are now basically in a 3
| wheel car and steer accordingly.
| Zak wrote:
| Typical sidecars pivot to allow a motorcycle to lean
| normally, so it's still countersteering. Rigidly-attached
| sidecars are used for some kinds of racing; those
| fundamentally steer like cars, though the "passenger"
| typically shifts their weight quite a bit to optimize
| handling.
| Abimelex wrote:
| 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
| tbyehl wrote:
| 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)
| amelius wrote:
| Isn't it illegal to indicate that you turn right, but then still
| go left first?
| analog31 wrote:
| It's much more subtle than that. Countersteering merely nudges
| the bike a tiny bit, basically throwing it out of balance so it
| leans into the turn. The reason why it's mentioned as being
| counterintuitive is that it's even too slight for someone to
| notice if they're watching you ride. And people who have been
| riding for a long time may be doing it without realizing what's
| happening in detail.
|
| In fact I suspect that you also countersteer to ride straight,
| i.e., making the slight corrections that keep you on a straight
| course.
| wruza wrote:
| There's no realistic way to drive straight (unstable
| equilibrium), so "straight" is really waving around it
| constantly. People who ride on easy mode (i.e. no hard tricks
| or turns) just learn to wait for a correct phase to start
| turning without realizing it.
|
| You don't have to steer anywhere to start a turn, in a sense.
| You're always turning and only have to stop countersteering
| at the right moment.
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(page generated 2023-03-05 23:00 UTC)