Why countersteer causes leaning

[BMW Triumphant]

It's been a long time since 1st year engineering physics. I wanted to really understand countersteering. Naturally, I went to Wikipedia and found a great graphic. I hope it displays or at least lets you click on it.

http://upload.wikimedia.org/wikipedia/commons/6/68/Gyroscopic_precession_256x256.png

A bike wheel has no gimbal pivot. But, the bottom of the wheel is held on the road and the top of the wheel can move, that is, lean.

I think this is the best illustration I have found, what do you think?

[EXR911]

It's been a long time since 1st year engineering physics. I wanted to really understand countersteering. Naturally, I went to Wikipedia and found a great graphic. I hope it displays or at least lets you click on it.

http://upload.wikimedia.org/wikipedia/commons/6/68/Gyroscopic_precession_256x256.png

A bike wheel has no gimbal pivot. But, the bottom of the wheel is held on the road and the top of the wheel can move, that is, lean.

I think this is the best illustration I have found, what do you think?

The front wheel out-tracks to the opposite side to which forward handlebar pressure is applied and the tire patch is then located off the centre line of the tire.

PT9766

[BMW Triumphant]

For very small steering head rotation, your explanation would not work. Did you look at the picture? It shows why the wheels lean.

The leaning comes first; outtracking will take a bit of time; outtracking could be done without any leaning, I think, for small angles, on an instantaneous basis.

[kthutchinson]

The best description of motorcycle dynamics I've found is in John Robinson's book Motorcycle Tuning: Chassis. He uses classical Newtonian physics and explains the difference between slow speed turns. where you don't countersteer, and higher speed turns where you do.

[ANDYVH]

The way I understand countersteering, is to realize the bike does not lean at the contact patches of the tires, as if the contact patches were the center line of a hinge. Imagine a centerline, running fore/aft through the bike, roughly just above the level of the cylinders, in the center of the bike. When the portion of the bike/rider combination goes in one direction left or right above the line, the rest of the bike/rider combination below that line has to goe the other way to balance.

Simple Newtonian physics, equal and opposite forces. Now, understanding that, if the front tire were slightly deflected off the center path to one side or the other (it being part of the bike/rider combination below the line), the upper portion of the bike/rider combination has to go the opposite way to maintain balance. Using that knowledge, it becomes very clear that in order to make a motorcycle lean accurately and quickly, the rider must steer the front tire off center of the "line". It also becomes very clear that new riders with no knowledge of motorcycle dynamics, easily crash when they try to "steer" a bike like a car and get the opposite result they thought they would get.

It also explains how we learned to ride a bicycle when very young. We had no concept of intentional countersteeing, and we wobbled/wiggled like crazy as we intuitively steered the bike like our eyes would direct us to do. But once the brain clicked onto the spatial idea of balance like it does when we learned to walk upright, then suddenly we gained balance and leaning control on a bicycle. Same principle on a motorcycle. Difference though, is the bike weighs MUCH more than the rider, so the rider must make direct intentional input, countersteering, to make the bike/rider combination lean as intended. It also explains why countersteering input is not needed for all riding, and why some people claim they can make the bike lean without countersteering.

To a point they are right, you can make a bike lean without DIRECT countersteering input. But ANY motorcycle lean is the result of either direct or indirect countersteering input. Indirect input is the result of the upper body "leaning into the turn" like some riders claim is their method to make a bike lean. Again, back to the "line", because the action of the rider leaning into the turn causes a force off center of the line that the bike reacts to by moving in the opposite direction. However, it is a slow method to make a bike lean. That is where the unknowing/untrained rider can get in trouble, when they expect the bike to lean accurately and quickly just by leaning the upper body into the turn. Then they get rigid at the grips and don't allow the front tire to move off center of the line, and the bike runs wide. Body lean countersteering is just not quick enough.

The "line" is like the horizontal frame of the gimbrel shown in the original post, and the "tire" rotates left and right around that frame. Except in the case of a bike in motion, we have the bike/rider in combination "rotating" around that line.

[sedanman]

Actually in a low speed turn there is a momentary countersteer to initiate the turn, I didn't think so until I saw this video. http://www.youtube.com/watch?v=OLzB5oriblk . Once the bike is leaning the bars must be turned into the turn to get the wheels back under the centerline of the bike. At higher speeds another force comes into play where the shape of the contact patch of the tires wants to force the tires back under the bike. For lack of a better description of this force I refer to it a "scrub thrust" . This is probably the best video I found to demonstrate countersteering, http://www.youtube.com/watch?v=1_A8k58ysSw&feature=related

[walterK75]

Some people call this push steering because you push the handlebar forward on the side to which you want to turn: right forward for right; left forward for left. See David L. Hough's Proficient Motorcycling for his explanation.

[BMW Triumphant]

snip outtracking could be done without any leaning, I think, for small angles, on an instantaneous basis.


I have rethought this part of my post; It is incorrect. Let me try again.

The original post had a link to a diagram. I still like the diagram as it shows the reason for a wheel to lean due to countersteering. In the diagram, it would be a right turn situation.

A bit of countersteering to the left as in the diagram would cause a bit of lean to the right for front and back wheels. More countersteer, more lean. Less countersteer, less lean.

At the start of the turn, the front and rear wheels have the same track, assuming proper alignment.

With a bit of countersteer, the front wheel is no longer completely aligned with the rear. As the front wheel rotates, the track of this wheel will be more and more to the left (in a right turn). Hence, outracking is not instantaneous, but takes time to develop as the wheel rotates.

At some point, if the rider wishes to stop the turn and resume straight ahead travel, the countersteering must cease. As it does so, the leaning will lessen the turning will cease, and at the end, with neutral steering, front and rear tracks will be the same.

However, the bike may not be travelling in the original direction. That would require a symmetrical left turn as well.

When the bike is leaning, gravity can be said to act through the centre of mass which will be to the right of the contact patch in a right turn. This gives rise to a horizontal force acting on the contact patch to provide the centripetal force pointing right, to the centre of the turn radius at any given instant.

There, that is what I wanted to say ...

I believe countersteer effects do increase with rotational speed increase. There is no lower threshold as such, just a smooth and continuous increase as speed rises from dead slow to slow to faster.

Tire flex and suspension effects have been ignored, but they would have real impact on the above I'm sure.

But, once again, it was the diagram that was so appealing to me that it prompted the original post.

[LuckyGrownup]

I think you are right. I have tired to counter-steer on a mountain bike. It doesn't work that well on mountain bikes that have 19" wheels. My guess is GS riders with their larger wheels might not have the same counter steer feel an RT rider would have. The RT has a smaller front wheel. In theory, you wouldn't have to go as fast to counter steer a bike with a smaller wheel. The smaller wheel spins faster and creates a greater gyroscopic force. Likewise, a mountain bike with a 19" wheel that is super light weight would have to go much faster to get a counter steer.

[kthutchinson]

Motorcycles don't lean due to gyroscopic precession; they lean due to the lateral force at the contact patch due to tire slip angle and camber thrust.

Gyroscopic forces can be completely eliminated by some tricky engineering. For example, one engineer designed a motorcycle brake system where the front rotors rotate in the opposite direction from the front wheel at twice the speed (Link (http://www.reverserotatingrotors.com/)). This significantly reduced the gyroscopic effect of the front wheel, but the bike handles fine (I'm not sure I buy all the developer's claims, however).

[oldnslow]

Any helicopter mechanics or pilots out there? They could add to the discussion and explain why increasing the pitch of the rotor blades at certain points in their circle of travel will cause the copter to move in a direction that is 90 degrees away, in the direction of travel of the spinning blades, from the area that the pitch is changed...

We did this experiment 'back in the day' Hold a fast spinning bicycle wheel with both hands, like you are the forks of a bike. Hold it with your arms pointing straight down, rotate your arms like you are turning and watch which way the wheel wants to tip. Didn't believe it till I tried it!

[BMW Triumphant]

Motorcycles don't lean due to gyroscopic precession; they lean due to the lateral force at the contact patch due to tire slip angle and camber thrust.

(snip)



Ok, I looked up slip angle and camber thrust in Wikipedia. Camber thrust was the clearest.

At http://en.wikipedia.org/wiki/Camber_thrust

I read, in part,

Camber thrust is generated when a point on the outer surface of a leaned and rotating tire, that would normally follow a path that is elliptical when projected onto the ground, is forced to follow a straight path due to friction with the ground. This deviation towards the direction of the lean causes a deformation in the tire tread and carcass that is transmitted to the vehicle as a force in the direction of the lean.

Ok, that makes sense and that force in the direction of the lean is the centripetal force that creates the turn.

However, I do believe that the "leaned and rotating tire" obtains the lean because of countersteering causing gyroscopic forces to lean the wheel. At that point, camber thrust operates as above.

I'm open to other ideas to how the wheel could obtain lean, if someone has something to offer... :scratch

[oldnslow]

Ok, I looked up slip angle and camber thrust in Wikipedia. Camber thrust was the clearest.

At http://en.wikipedia.org/wiki/Camber_thrust

....
Ok, that makes sense and that force in the direction of the lean is the centripetal force that creates the turn.

However, I do believe that the "leaned and rotating tire" obtains the lean because of countersteering causing gyroscopic forces to lean the wheel. At that point, camber thrust operates as above.

I'm open to other ideas to how the wheel could obtain lean, if someone has something to offer... :scratch

You are correct...with a fast rotating front wheel, with substantial mass, when you turn the handle bars to the left, that is the same as applying a force to right side of the leading edge of the tire, and a force to the left side of the trailing edge. This force is transmitted 90 degrees in the direction of the wheels rotation, causing the wheel to lean to the right, as if a force was pushing to the right at the top of the tire and pushing to the left at the bottom of the tire. Traction prevents the tire from slipping out from under the bike, so the force causes the bike to lean to the right. Then other forces come into play.

Im no physics expert, and could be wrong. Just conversing here. I'm a single dad so I enjoy an occasional conversation that doesn't revolve around XBox or Facebook!

[35634]

Countersteering for idiots:

turning the handlebars at speed will cause bike to fall down

turning less will cause bike to fall down less, or "lean"

a leaning bike is a turning bike

Thinking about all this while riding may cause you to fall down

Thinking less may help:D

[kthutchinson]

When the handle bars are turned left, a lateral force to the left is generated at the contact patch due to tire slip. This is the same force generated in your car when the steering wheel is turned left. This force creates a rolling moment to the right, causing the motorcycle to lean right.

[lkchris]

Yeah it's all kind of "scientific," but there's a simpler way to think of it.

If your bike is going to lean left, the left handgrip is going to be lower, i.e. closer to the ground than the right one.

To get it that way, you're going to have to push it down.

Vice versa, of course.

You can "wheelbarrow" through a curve with the bike remaining upright/not leaning but you're not going to be able to do it at more than 1 mph or so. Probably less (haven't tested).

[sedanman]

A very simple way to think of it is like a little kid pretending to be an airplane, "fly" the bars down the road like you would an airplane wing. Try it, it's kind of fun.

[BMW Triumphant]

When the handle bars are turned left, a lateral force to the left is generated at the contact patch due to tire slip. This is the same force generated in your car when the steering wheel is turned left. This force creates a rolling moment to the right, causing the motorcycle to lean right.

I agree about the lateral force and believe this is the centripetal force that is required for the bike to turn.

I am not sure the direction is correct as turning bars to the left should cause a right turn and this requires a centripetal force to the right and this force has to occur at the tire patch...

I do not understand how the force causes a rolling moment which causes the bike to lean. When not leaning, the force of gravity is perpendicular to the road and the slip angle force is at right angles to that. Vectors at right angles can't have any components one upon the other, so they are independent.

I'm still of the mind that gyroscopic effects cause the lean and the lean plus the centripetal force caused by the slip angle and / or castor sources you mention are both required.

But, if you can clarify or add something, please do so. :scratch

Can you help me understand your model?

[BMW Triumphant]

I may be able to add something...

Further research reminded me that a force on the tire at the road is lower than the centre of mass of the bike. This force is equivalent to a type of force called a couple and the couple would cause a rotation around the centre of mass.

The diagram at http://en.wikipedia.org/wiki/Couple_(mechanics) would seem to support a slip force to the right causing a rotation that would be a lean to the right.

So, at this point, I would say both the gyro forces and the slip forces contribute to the leaning of the bike. I am satisfied I have the directions correct and they both point to the centre of the turn, ie, provide the required centripetal force.

What I don't know is how big the forces are, one relative to the other.

Tires are pretty stiff and distorting them takes a lot of energy. But, wheels rotate quickly and might have appreciable gryroscopic forces. That would depend upon the wheel / tire system's Moment of Inertia, which could be calculated by someone whose calculus skills are a bit more recent than mine if they had the data.

So, unless there are more facts, I am going to say both of these forces contribute, but I don't know which is greater. :scratch

[kthutchinson]

I agree about the lateral force and believe this is the centripetal force that is required for the bike to turn.

I am not sure the direction is correct as turning bars to the left should cause a right turn and this requires a centripetal force to the right and this force has to occur at the tire patch...

I do not understand how the force causes a rolling moment which causes the bike to lean. When not leaning, the force of gravity is perpendicular to the road and the slip angle force is at right angles to that. Vectors at right angles can't have any components one upon the other, so they are independent.

I'm still of the mind that gyroscopic effects cause the lean and the lean plus the centripetal force caused by the slip angle and / or castor sources you mention are both required.

But, if you can clarify or add something, please do so. :scratch

Can you help me understand your model?

BMW Triumphant,

My post #15 explains how an initial countersteering input to the left causes the bike to lean right. As the bike leans right, the countersteering input is removed and the bars are actually turned slightly to the right, into the turn. The lateral force at the contact patch is now to the right, and this is the centripetal force that causes the bike to turn.

Gravity will be trying to pull the bike farther over to the right, and the centripetal turning force will be trying to roll the bike upright to the left. When these rolling moments balance the bike will maintain a constant lean angle.

For another good technical explanation, see chapter 4 in Tony Foale's excellent book Motorcycle Handling and Chassis Design. He also gives an explanation of the role of gyroscopic effects in stability.

[AKsuited]

Yeah it's all kind of "scientific," but there's a simpler way to think of it.

If your bike is going to lean left, the left handgrip is going to be lower, i.e. closer to the ground than the right one.

To get it that way, you're going to have to push it down.Vice versa, of course.



Sorry, but that's exactly...wrong.

You don't push the left or right grip down, you push it forward.

And that's all you really have to know about countersteering: push right, go right, push left, go left.

Harry

[pffog]

Here we go again............................................. ...................

[oldnslow]

You know, to be quite honest, I had never gave this any thought until last night. When I want to turn, I just turn. 99% of the time I don't even have an actual thought to 'push' or 'turn' anything, the bike just follows the road. :D

[maxscycle]

I read a lot of explanations, a lot of scientific arguements. But the one I like best is the one I use in an MSF course when we are talking about pressing the left handgrip forward to get the bike to go left........
"Folks, you don't have to understand exactly how an airplane flies through the air, you only have to know that it does. And like wise, you don't need to know how a bike countersteers, only that it does."
This simply explaination stops probably 98% of the puzzled looks in a class.
The other 2%, I ask them to ask me again during break.
95% of the time, they forget to ask.
max

[henzilla]

And like wise, you don't need to know how a bike countersteers, only that it does."


My take on it as well...I don't over analyze the physics of the action...just know it works and that's all I need :D
But y'all continue on...

[ANDYVH]

When it all comes down to it, there comes a time you have to make the motorcycle turn, period. That is done by countersteering of some form, period.

When the day comes that you don't use countersteering, you WILL run wide, run off the road, hit the object you don't want to hit, loose control, period.

So to riders who say they don't/never use some form of countersteering, they are either unaware they are doing it, or they simply have gotten by,.....so far. But it is very true that for 90% of riders: don't over analyze it, just do it, learn it, use it.

Years ago my orthopedic surgeon was a student in my MSF class. A very smart man, intelligent, and,...I failed him in the course because he would NOT accept the concept that the bike would go in the direction he pressed. Even after I told him, "don't think about it, just do it, get the feedback from the bike, and use it." He failed the swerve manuever everytime because his brain said "steer like a car" and by the time the bike moved, and he corrected, he would have hit the obstacle. I spent more time with him one-on-one later and he did get it and got his license. So don't over-think it, just do it and enjoy the results!

[sedanman]

In my youth I had a Honda 650 NightHawk. I just rode it without thinking about how it worked I just "leaned to turn" and it turned..................until that time when it didn't. I was in a wide sweeping turn at the postted speed of 30 mph and the bike would NOT TURN ! I ran off the road and onto someones lawn. I kept the bike upright and didn't tear the guys lawn up but I was STUMPED as why to leaning didn't make the bike turn. Then I get enloghtened about countersteering.
Not overthinking it is one thing, but you MUST understand it to at least some degree to avoid disaster.

[BMW Triumphant]

As the bike leans right, the countersteering input is removed and the bars are actually turned slightly to the right, into the turn.


Removing the countersteering input in one direction would seem to imply that a countersteering input is applied in the other direction. There is no switch to turn the effect of countersteering on or off, I believe. Also, if the wheel is turned into the turn, why is this definitely not countersteering the other way, causing the bike to first straighten up before leaning the other way? Even if gyroscopic effects are zero, this question still has validity.

By the way, for those kind folks who have provided non-technical input, I do practice countersteering and have no actual operational problem in my riding, except always wanting to get more skilled, or at the beginning of a long winter, getting my skills back to where they were. I like to understand the technical reasons for what my bike does. You need not have the same interest, of course.

My original post was to provide a source for a very good diagram of a gyroscope that might help folks understand how countersteering left resulted in the wheel and bike leaning right. It was not to prompt a discussion of whether countersteering was necessary, by now most of us know it is.

New information has been suggested that gyroscopic effects are not responsible for leaning, or not the principle cause for leaning. If there is a reader who knows a web site where this topic is explained, I would be grateful for the information.

I would also be grateful to learn about the claim that countersteering is only initial, because I can't understand that.

[AKsuited]

You know, to be quite honest, I had never gave this any thought until last night. When I want to turn, I just turn. 99% of the time I don't even have an actual thought to 'push' or 'turn' anything, the bike just follows the road. :D

The problem with that, Mike, is what do you do when you need to swerve? That's when you need to countersteer like mad.

Harry

[oldnslow]

The problem with that, Mike, is what do you do when you need to swerve? That's when you need to countersteer like mad.

Harry

I guess my point was that I don't conciously (sp?) know what I am doing, I just do it. If I had to 'think' about swerving, it would probably be too late. This like trying to explain how goalie stops a hockey puck. Its physically impossible if he were to think about it, he just does it.

Ever notice how your bike will go the opposite direction you want it to go; just ever so slightly; when you do a quick and deliberate turn at speed? A real small zig, just before you zag? That's the countersteering working.

[pipestone]

I still don't understand it and have been doing it for 45 years :scratch

[sedanman]

Removing the countersteering input in one direction would seem to imply that a countersteering input is applied in the other direction. There is no switch to turn the effect of countersteering on or off, I believe. Also, if the wheel is turned into the turn, why is this definitely not countersteering the other way, causing the bike to first straighten up before leaning the other way? Even if gyroscopic effects are zero, this question still has validity.

By the way, for those kind folks who have provided non-technical input, I do practice countersteering and have no actual operational problem in my riding, except always wanting to get more skilled, or at the beginning of a long winter, getting my skills back to where they were. I like to understand the technical reasons for what my bike does. You need not have the same interest, of course.

My original post was to provide a source for a very good diagram of a gyroscope that might help folks understand how countersteering left resulted in the wheel and bike leaning right. It was not to prompt a discussion of whether countersteering was necessary, by now most of us know it is.

New information has been suggested that gyroscopic effects are not responsible for leaning, or not the principle cause for leaning. If there is a reader who knows a web site where this topic is explained, I would be grateful for the information.

I would also be grateful to learn about the claim that countersteering is only initial, because I can't understand that.

There are 3 basic levels to understand. Low speed, mid speed, and high speed.
At low speed there is almost no camber thrust available to push the tires back under the bike. So at low speed you countersteer to get the bike to fall into the turn then you have to steer the front wheel to drive it back under the bike to keep from falling all the way over. At low sppeds countersteering is only initial. At high speeds there is a lot of camber thrust to push the tires under the bike so it takes very little input on the bars to control the turn. At higher speeds you have to keep countersteering to offset the camber thrust. In a high speed turn you do turn the bar in the direction of the turn when you want to stand the bike back up, just not nearly as much as at slow speeds. Mid speed is the murky area where the rules change and I can't seem to find words to explain it clearly (as if I have been clear up to this point, lol )
I am also fairly certain that bike beginning to fall has less to do with the gyroscopic effects and more to do with front end geometry.

[maxscycle]

Years ago my orthopedic surgeon was a student in my MSF class. I failed him in the course because he would NOT accept the concept that the bike would go in the direction he pressed.


That's funny, not accepting the concept is not a grading criteria of Eval #2.
And if he maxed out eval #2, he still should have passed unless something else added up to "sorry, but......."
Also, try to remember, you didn't fail him. You only kept score. He/she rode as they rode.
max

[ANDYVH]

Guess I should clarify that. It wasn't that he failed because he did not accept the "concept", but he failed because he could not/would not apply the concept. True that he is the one that failed. He failed the swerve on both attempts, first was too slow and he "hit" the corner of the obstacle. His second attempt speed/time was ok, but again he hit the corner of the obstacle. 10 points right there.

Then in the 135 degree turn, again because of trying to "steer" the bike through the turn he went outside the boundary and was slow. By then he amassed more than enough point to fail himself. His son and daughter in the same class both passed easily.

[henzilla]

I am also fairly certain that bike beginning to fall has less to do with the gyroscopic effects and more to do with front end geometry.

I vote gravity:laugh

[sedanman]

I vote gravity:laugh

Gravity cannot be ignored, it is a LAW after all! To be specific, I believe the DIRECTION of the fall is influenced by front end geometry and the direction in which the wheel is pointed.

[BMW Triumphant]

I seem to have lost the ability to read a technical article carefully enough the first time...or maybe I only thought I once had that ability.

Went back to an article I had read previously:

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

Several interesting points:

1) A steering torque is different from a steering angle.
2) A steering torque is what we apply first and the gyro forces are instantaneous to cause lean. Gyro forces are about 12% of camber thrust forces.
3) To stop the bike from falling over, the article says we adjust the steering angle to be in the direction of the turn. [This has to be a bit of reverse countersteer.]
4) Depending on speed, the steering torque may have to be maintained in the initial direction, left for a right turn, even if the steering angle through the right turn is to the right.

For the technical guys, could you have a look at the article and let me know your thoughts on it?

This is almost making sense, and most of my questions have been answered.

[Fourcats]

I have mostly just accepted the term, believing that the forces in question do a good job of getting me around...The diagram is great, simple and confirms my beliefs. :thumb

[ANDYVH]

Spent yesterday afternoon out on a frozen lake doing a TT course on my ice bike (Suzuki GN400 converted to an ice-bike/flat-tracker). Interesting study in the reaction of countersteering and steering with the throttle.

Even on ice (1200 ice screw heads per tire) countersteering still applies, though the feel is of course a bit different. On some turns I experimented with purposely "steering" into the turn while leaned over, one foot out/motocross style. I could almost instantly feel the rear wheel push out and then I could countersteer into the slide.

But feet up, leaned into the turn, throttle on, and countersteering definitely still works! My ice bike has fat 18" knobby tires front and back, and each tire alone weighs over 25 pounds, so there is a lot of gyroscopic force there, which in some cases required a lot of countersteering input to get the bike to respond. One thing for sure, one thing you don't do when leaned over and with the rear end sliding is chop the throttle shut, instant traction has an amazing leverage effect. At least on the ice with some snow on top it is more forgiving.