Countersteering Confession

[Skyryder]

The bike isn't horizontal, it's like a vertical pole except because it's got two wheels, it can only fall over sideways, not forwards and backwards as well (like a pole would).

Call me pedantic but this needs a correction. The balancing pole is to all intents and purposes stationary with one point of contact. It is vertical.

The bike has two ponts of contact. This changes the equation from vertical to horozontal. Both are affected by gravity and fall downward

A uni cycle would be in the same catogory as the pole with a single contact point.

I agree that Le Mans stated the definitive answer to this question that counter steering occurs at the first level of turning. It iniates the turn.

Skyryder

[Jamezo]

EDIT: This is in response to MartyB

Wrong wrong wrong wrong wrong.

I'm assuming you are quite well versed in gyroscopic theory, so this'll be easier.

Assume, for the moment, that the force that leans the bike and wheel over does not come from a precession force:

Now we have a forwards-rotating wheel, being made to turn - for different reasons - sideways.

You understand, correctly, that a force applied to a gyroscopic object produces a torque in a plane 90 degrees advanced in the plane of the axis of rotation.

So consider the force that is making the wheel tip sideways, say left. Rotated in the plane of the axis of rotation by 90 degrees, this looks like a counter-clockwise torque.

Note that this is in opposition to the clockwise counter-steering input that you would be applying to turn the bike left!

For the actual matter of what causes the sideways movement, you'll have to look back at the actual contact forces involved. Check out http://www.rider-ed.com/tips/motorcyclestability.htm or something.

Note that the opposition precession force is always less than the input required to affect a turn, or else you'd never be able to turn!

This is also why that guy with the counter-rotating rotors is onto the right idea; the precession force is NOT what steers the bike, it is a damping influence on the rate of rotation.

[vtec]

Here's an idea to simplify it for marty.

Try imagining riding a motorcycle with the latest high tech carbon fibre kevlar wheels. And just imagine for theory's sake that the wheels on the bike weigh absolutely nothing. Now this gets rid of ALL of the gyroscopic effects from the wheels. Now, when you are riding this bike at say 100k/hr, will you still countersteer to lean the bike and maintain the lean? Of course you will. Gyroscopic precession is a factor, but not the main one.

It's a combination of castor angle and the geometry of the tyres (and momentum in one direction) that makes the bike want to stand up (at high speeds).

Unless I'm missing something gyroscopic effects merely resist changing of angle. Once that angle has changed, this becomes the new angle at which the gyroscopic effect will resist movement from.

At low speeds, you still have to do the balancing act to turn the bike, if you want to go right, you have to move the wheels left underneath you so that the bike leans to the right. This happens at all speeds, but can be negated by putting your feet on the ground. However the dynamics of the bike at low speeds will mean that if you are leaning it, it will want to fall over, so you have to put in opposite force to normal countersteering to get it to maintain a lean angle at low speeds. So as Jamezo said, it initiates the turn, but at high speeds you need to keep countersteering to maintain the turn due to the bike wanting to straighten up and this is caused by the increased momentum of the motorcycle combined with the castor angle and the tyre geometry, and partially gyroscopic effect.

And erik's example of the broomstick is still useful if not perfect. Balancing a bike is actually more simple than a broomstick as you only have one axis of leaning to correct for by countersteering the wheels underneath you.

Another example is those remote control motorbikes. The wheels on those weigh next to nothing, and they want to straighten up once over about 5k/hr, this is due to the castor angle and tyre geometry, and next to nothing to do with gyroscopic precession, as the wheels weigh next to nothing, and have a tiny radius.

[Jantar]

Here's an idea ...
Try imagining riding a motorcycle with the latest high tech carbon fibre kevlar wheels. And just imagine for theory's sake that the wheels on the bike weigh absolutely nothing. Now this gets rid of ALL of the gyroscopic effects from the wheels. .

It also makes the bike impossible to ride. What do you think keeps the bike from tipping over? It surely isn't the rider's remarkable sense of balance.

[vtec]

It also makes the bike impossible to ride. What do you think keeps the bike from tipping over? It surely isn't the rider's remarkable sense of balance.

The castor angle and momentum of the bike, combined with tyre geometry.

http://en.wikipedia.org/wiki/Caster_angle

Have a good read in there, they even discuss motorcycles.

Edit: it seems that these articles have more info
http://en.wikipedia.org/wiki/Countersteer
http://en.wikipedia.org/wiki/Rake_and_trail

P.S. Rake and trail is similar to castor angle, but the Rake and trail article is way more relevant to this discussion. That is what explains why a bike wants to straighten up at speed.

[Jantar]

Sorry, but very early bikes had square profile tyres, and many had the castor angle buil out so that there was none. Castor angle and tyre profile are two of the components of bike steering stability, but have almost no effect on balance.

[Pieyed]

I guess everyone looked outside and saw the sun and went for a ride to test their theories Tui.

Been for a ride today and only wet at the begiinning and the end.

[marty]

Here's an idea to simplify it for marty.

Try imagining riding a motorcycle with the latest high tech carbon fibre kevlar wheels. And just imagine for theory's sake that the wheels on the bike weigh absolutely nothing. Now this gets rid of ALL of the gyroscopic effects from the wheels. Now, when you are riding this bike at say 100k/hr, will you still countersteer to lean the bike and maintain the lean? Of course you will. Gyroscopic precession is a factor, but not the main one.

It's a combination of castor angle and the geometry of the tyres (and momentum in one direction) that makes the bike want to stand up (at high speeds).

Unless I'm missing something gyroscopic effects merely resist changing of angle. Once that angle has changed, this becomes the new angle at which the gyroscopic effect will resist movement from.

At low speeds, you still have to do the balancing act to turn the bike, if you want to go right, you have to move the wheels left underneath you so that the bike leans to the right. This happens at all speeds, but can be negated by putting your feet on the ground. However the dynamics of the bike at low speeds will mean that if you are leaning it, it will want to fall over, so you have to put in opposite force to normal countersteering to get it to maintain a lean angle at low speeds. So as Jamezo said, it initiates the turn, but at high speeds you need to keep countersteering to maintain the turn due to the bike wanting to straighten up and this is caused by the increased momentum of the motorcycle combined with the castor angle and the tyre geometry, and partially gyroscopic effect.

And erik's example of the broomstick is still useful if not perfect. Balancing a bike is actually more simple than a broomstick as you only have one axis of leaning to correct for by countersteering the wheels underneath you.

Another example is those remote control motorbikes. The wheels on those weigh next to nothing, and they want to straighten up once over about 5k/hr, this is due to the castor angle and tyre geometry, and next to nothing to do with gyroscopic precession, as the wheels weigh next to nothing, and have a tiny radius.

i never said GP had anything to do with keeping the bike upright. gyrosopic rigidity aids in keeping the bike upright, but it's mostly balance of the rider.
gyroscopic rigidity resists turning, but GP aids it.

and i'm imagaining, and i've imagined a ski doo on the snow. it's as close to your theoretical weigh nothing wheel. try pulling the right handlebar to go left. it won't.

[vtec]

Sorry, but very early bikes had square profile tyres, and many had the castor angle buil out so that there was none. Castor angle and tyre profile are two of the components of bike steering stability, but have almost no effect on balance.

Don't apologise. I'm guessing that square profile tyres are fine for the mud tracks that very early bikes had to deal with, but they wouldn't be suitable for concrete or tarseal at anything over 20k/hr.

And you can't tell me that a bike with no castor angle was a brilliant handling self balancing wonder, because it just would not be true. No castor angle, would mean that ALL of the balancing would be done from rider input. Doable, but not fun.

Think of it this way. When you lean a bike with a castor angle, it puts sideways force on the patch of the wheel that touches the ground in the upwards direction. This patch of tyre is behind the line of the front forks meaning that it will effectively push the bars in the direction opposite to countersteering which is why you need to countersteer to get the bike to lean back down. So castor angle does affect the balance of the bike.

[vtec]

i never said GP had anything to do with keeping the bike upright. gyrosopic rigidity aids in keeping the bike upright, but it's mostly balance of the rider.
gyroscopic rigidity resists turning, but GP aids it.

and i'm imagaining, and i've imagined a ski doo on the snow. it's as close to your theoretical weigh nothing wheel. try pulling the right handlebar to go left. it won't.

Using a ski doo is completely different from my example, cause they are wide enough that you don't need to balance them, this doesn't affect any of the arguments... That's almost like trying to use a car as an example... pointless with regards to countersteering a motorbike... go back to using my example of the weightless wheels, and try to imagine what would happen.

The fact that the bike wants to straighten up is the reason why you need input from the rider in the form of countersteering to get it to lean back down, so effectively in saying that the gyroscopic precession doesn't make the bike want to stand up, you are saying that it's not what makes the rider need to countersteer.

Edit: Also note you stated that the bike is kept upright by the balance of the rider? This is wrong, the bike is kept upright by the castor angle mostly, of the bike when it is at speed. You can affect it by either countersteering or moving your weight to either side, so that the castor angle effect is overcome to a certain degree.

[terbang]

Here's an idea to simplify it for marty.

Umm no you are complicating it for yourself. Marty is correct it is Gyroscopic precession that produces the rollng motion on the bike.
Other features such as trail and gyroscope rigidity help to make the bike stable (there is a difference between control and stability). But the rolling motion toward or away from any lean angle or adjustment of lean angle is primarily a result of Gyroscopic precession. Thats what countersteering does and we all use it whether we are aware of it or not.

[terbang]

Edit: the bike is kept upright by the castor angle mostly, of the bike when it is at speed. You can affect it by either countersteering or moving your weight to either side, so that the castor angle effect is overcome to a certain degree.

Not correct. Caster angle and trail are there for directional stability. It is gyroscopic rigidity that keeps the bike upright when moving and the side stand that does it when it is stationary.
However this discussion is not about stability it is about countersteering which is control..

[vtec]

Not correct. Caster angle and trail are there for directional stability. It is gyroscopic rigidity that keeps the bike upright when moving and the side stand that does it when it is stationary.
However this discussion is not about stability it is about countersteering which is control..

Not Correct. Gyroscopic rigidity merely maintains a rotating objects direction and angle. Which would mean that if you leaned it down, it would stay down, not straighten up. There is other forces at play that cause it to straighten up.

A good example is like comparing it to a suspension component. The Gyroscopic rigidity acts like the dampener, and the caster angle acts like the spring in a rear shock. Only difference is that the shock works only up and down, whereas caster and GR act from left to right on both sides of the bike.... Try going at low speeds and you will notice that it is very easy to flick the bike from side to side, and at a certain speed it will oscillate from side to side, that is the caster angle acting like a spring without any dampening from the GR, at high speed with GR, the steering will get harder and harder to turn, and nearly impossible to flick from side to side, this is because both the GR effect and the caster angle effect increase greatly at speed. It's like turning up the dampening and the springrate heaps in your rear shock.

This discussion is relevant, because it is discussing the reasons behind why you need to countersteer a bike.

[MacD]

This is the short version.

http://www.vf750fd.com/blurbs/counter.html

Countersteering works by moving the wheels out from under the bike.



Once the bike is leaned over, the trail of the front end causes the front wheel to turn into the curve, and the round profile of the tires causes the bike to experience camber thrust steering (similar to rolling a cone, which travels in a curved path), which cause the bike to go around the curve. When it's time to straighten out, countersteering is again used, this time to move the wheels back underneath the center of mass of the bike and cause it to stand up.

I'm lining up with Lemans and Jamezo on this one. The gyroscopic effect of the spinning wheel has much less effect on riding than people claim. Bikes have been built with counter-rotating wheels-within-wheels to cancel the gyroscopic effect and they still behave much like an ordinary bike.

Countersteering does momentarily move the front wheel out of line, as would be expected by the process of rotating the bars in the opposite direction to your intended turn. It is a useful technique for avoiding small objects on the road as you can kick your front tyre out and around the object with a countersteer input. The bike starts to roll and the front wheel returns to the appropriate track for the turn. Turning results from what people have termed camber thrust (the rolling cone idea) and slip angle (how much your tyres effectively slip across the road during the turn).

Anyhow, engineers actually study and model this stuff (Imperial College London) and write review papers on it (public download of manuscript).

See around p14 for a discussion of gyroscopic forces and p17/18 for torque steering/countersteering.

Personally I believe the bike stays upright and the world leans, but that's just me!

[Jamezo]

Further summary:

Precession forces only play a damping role when the bike is rolling. The way the 'gyroscopic inertia' manifests itself is through the counter-torque on the bars.

Physics wins yet again! Interesting stuff MacD.