Principle of steering a motorcycle (or bicycle)

[SCBuckeye]

Years ago, circa 1980, published in the BMWMOA was an article explaining the geometry of a motorcycle and how it tracked on the one hand, and how the principle of countersteering worked.

About 1-1/2 years ago, someone wrote in a letter to the editor with his explanation. He was correct on high speed steering, but was totally wrong when considering what happens at slow speed steering. I then wrote a letter to the editor with a correct explanation, which went unpublished for some reason (I think I know why). I also contacted the writer of the letter to the editor by phone, who, after listening to my explanation argued with me, and then hung up.

Since then, I have found a video explaining what ACTUALLY happens both at high speed AND at slow speed. Please check it out.

The key to understanding what is going on at ANY speed is Newton's principle of motion: that an object will stay in motion until it is acted upon by another force. This is what happens when one steers. When you rotate the handlebars to the left (CCW), the bike where it touches the ground (tire patch) will go left, but the mass of weight will stay going straight forward. The longer this happens will action will force the bike into a lean where gravity is forcing the mass of weight to fall over. When the centrifugal force matches the falling gravity force, this will create a manageable lean - at that time the rider will have to modify his steering to keep that equilibrium. Then, when wanting to go straight again, the rider will have to steer the "tire patch" back under the mass of weight to then get upright and go in a straight line.

Please watch this YouTube video which explains why this happens at ANY speed, not as the letter-to-the-editor author mistakenly wrote in his letter.

https://www.youtube.com/watch?v=C848R9xWrjc

Thanks,

 

[Omega Man]

I usually mention for a rider to put one hand on top of their head and steer with the other......then switch.
The results frequently amaze.
OM

 

[kthutchinson]

I wish folks would leave physics to physicists. The OP essentially attributes countersteering to gravity. Gravity certainly plays a part, but a small one (see chapter 4 of Tony Foale's book). If gravity is so important, please explain how countersteering out of a turn works. And one final thought. Centrifugal force is a myth!

 

[soocom1]

Well I am not going to get into a debate over physics, but I seem to remember that counter steering is based ont he principle of gyroscopics which is in of itself a entirely diff. component of physics.

But maybe Im wrong.

 

[kthutchinson]

I don't think there's anything to debate. Too many people attribute countersteering to gravity and gyroscopic precession. They both play a part, but only minor ones. Think about how little you have to turn the handlebars at speed to initiate a lean. The CG has barely moved, and the rate that the bars are turned so low that neither gravity or precession will have a major effect. As I stated earlier, I strongly recommend Tony Foale's book Motorcycle Handling and Chassis Design. Tony give excellent numerical examples to back up his assertions.

 

[soocom1]

Well, gravity aside, as it was explained to me in the most simplistic form is the ratio or more precisely the reciprocal of the curvature to contact area is what causes the whole mess.

This is a wholly simplified explanation to the forces at work, and quite frankly its so simple its too easy understand.


Again... just me.

 

[WalterK75]

Push handlebar right, turn right, push left, go left.

 

[kthutchinson]

Well, gravity aside, as it was explained to me in the most simplistic form is the ratio or more precisely the reciprocal of the curvature to contact area is what causes the whole mess.

This is a wholly simplified explanation to the forces at work, and quite frankly its so simple its too easy understand.


Again... just me.

If you mean the lateral forces generated at the contact patches, I completely agree.

 

[akbeemer]

Push handlebar right, turn right, push left, go left.

Until the Coriolis effect comes into play. Pretty sure that in Argentina it just the opposite.

 

[greenwald]

If it's OK with you, I'll just turn my head, press to initiate a lean in that direction and be on my way. That seems to have worked well for 37 years so far (not counting my years on the Schwinn).

 

[akbeemer]

I suspect the top ten riders in each of the MotoGP classes, World Superbike and every other racing series know very little about the physics of how a motorcycle turns. Yet, somehow they seem to get it done.

 

[SCBuckeye]

I wish folks would leave physics to physicists. The OP essentially attributes countersteering to gravity. Gravity certainly plays a part, but a small one (see chapter 4 of Tony Foale's book). If gravity is so important, please explain how countersteering out of a turn works. And one final thought. Centrifugal force is a myth!

Your attacks are not correct!

One needs to understand that the "tire patches" are where the motorcycle touches the road. When turning to the right, all you are doing is to steer the tire patches out to the right, but the mass of matter, following the rule from Newton's "things in motion will stay in motion unless moved upon by another force", will want to continue in a straight line, both forwardly and vertically. As the tire patch gets further out from the mass center of gravity, the mass of gravity will become more affected by the force of gravity, causing the mass to start to fall. As it does fall, the rider then compensates by modifying the steering to "balance" the downward force with the outward force.

I agree that the notion of "centrifugal force" is a myth, in that it is nothing more than Newton's law (above) being moved upon by being tied to a center (i.e. axle of a wheel, center of the radius of a turning vehicle, etc.) so the force wants to go straight, but can't due to the force of being tied to a center point (or the tire patches sticking to the ground moving in a circular way).

Explanation of how the force of gravity is being affected when coming out of a turn: (for those of you from "Rio Linda")

When in a turn and leaning where the downward force of gravity is being "equalized" by the straight force outward (i.e. centrifugal so-called), one can maintain that turn for as long as he wants to. However to straighten back up, the operator must act with a force greater than the force of gravity at that time to overcome the gravity. So, if going around a leftward circle, the operator merely steers MORE to the left - which in turn causes the tire patches to begin to go back directly under the mass of matter - to the point where they are directly under the center of the mass. At this point, the bike becomes vertical and then the operator changes the steering to straight-on so that the mass will then go in a straight line.

I just wish the people who make critical, unfounded comments would just learn to think!

Check the video I posted from You Tube and you can SEE what I am talking about both at high speed and at 2 MPH !!

 

[SCBuckeye]

I don't think there's anything to debate. Too many people attribute countersteering to gravity and gyroscopic precession. They both play a part, but only minor ones. Think about how little you have to turn the handlebars at speed to initiate a lean. The CG has barely moved, and the rate that the bars are turned so low that neither gravity or precession will have a major effect. As I stated earlier, I strongly recommend Tony Foale's book Motorcycle Handling and Chassis Design. Tony give excellent numerical examples to back up his assertions.

As the rider turns the bars, what causes the bike to lean? It has to be gravity where the tire patches NOT being directly under the C/G so the bike starts to fall and succumb to gravitational forces. At higher speeds this happens faster as it doesn't take much turning to get the tire patches out further and further. At slow speeds, it still happens but much more slowly. The only thing keeping the bike up is simply using other forces to overcome the gravity forces.

 

[83014]

As the rider turns the bars, what causes the bike to lean? It has to be gravity where the tire patches NOT being directly under the C/G so the bike starts to fall and succumb to gravitational forces. At higher speeds this happens faster as it doesn't take much turning to get the tire patches out further and further. At slow speeds, it still happens but much more slowly. The only thing keeping the bike up is simply using other forces to overcome the gravity forces.

I'm going to disagree. If gravity was the force that that causes the lean, then what force causes the bike to return upright when exiting the turn?

Entering a turn, the bike wants to continue in a straight line. Turning the wheel initially to the left, the bike will attempt to continue in a straight line. That force, not gravity, will cause the bike to lean to the right. With continued force on the handlebar, the bike will eventually low side. If the force on the handlebar is neutralized, then the bike will remain at that lean angle until opposite force on the handlebar causes the bike to right again followed by neutralizing the force to maintain the vertical position. Although your handlebar inputs will be required to maintain the desired angle while in the turn, only some of that is to resist the effect of gravity after the lean angle is established.

That's my version, anyway.

Doug

 

[AKsuited]

Consequences

I agree that it doesn't really matter what you think makes counter-steering work. What matters is what can happen if you don't understand counter-steering and are able to use it:

<iframe width="940" height="529" src="https://www.youtube.com/embed/ZUWViatY_LA" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

I once had a pirate patiently explain to me that counter-steering couldn't possibly work due to gyroscopic precession, and that in a room full of pirates, none of whom disagreed with him.

Push right, go right; push left, go left.

 

[Omega Man]

I have a feeling that some get confused over the term "push". After years of driving things with steering wheels or levers, I think most think they are actually pulling

That's why I always thought the example of riding with one hand on top of the helmet demonstrated the effect pretty well.

OM

 

[SCBuckeye]

I'm going to disagree. If gravity was the force that that causes the lean, then what force causes the bike to return upright when exiting the turn?

Entering a turn, the bike wants to continue in a straight line. Turning the wheel initially to the left, the bike will attempt to continue in a straight line. That force, not gravity, will cause the bike to lean to the right. With continued force on the handlebar, the bike will eventually low side. If the force on the handlebar is neutralized, then the bike will remain at that lean angle until opposite force on the handlebar causes the bike to right again followed by neutralizing the force to maintain the vertical position. Although your handlebar inputs will be required to maintain the desired angle while in the turn, only some of that is to resist the effect of gravity after the lean angle is established.

That's my version, anyway.

Doug

To help illustrate, draw a series of sketches of the bike with both a top view and a rear views showing the bike as it begins to turn and periodically throughout the turning operation. As you turn the hbars, the tire patch will begin to move from being directly under the C/G to either the left or right depending on which direction you are turning. As the tire patch gets further and further out from under the C/G, gravity forces the mass of weight down (do you ever ask why the C/G stands for "Center of GRAVITY" ??) If the rider continues to direct the tire patch out even further, the bike will fall down completely. But, to avoid that, the rider will re-adjust his/her steering direction just enough to equalize the downward force (gravity) with the outward force (for simplicity now, let's continue to call this centrifugal force). When done turning around the corner, the rider then steers the handlebars so that the tire patch goes back to being directly under the C/G - thus the bike resumes going in a straight line again.

 

[SCBuckeye]

Why is this good to know?

Some have poked fun at all of this as though it is not necessary to know - i.e. - just go and ride.

Well, it is good that SOMEONE understands!!

Also, I had a practical example of how this knowledge helped me.

When I first read about this steering principle, I didn't believe it. After all, I had been riding both bicycles and motorcycles for 25 years! I went out on my old /2 BMW and experimented. I found out that the principles that I thought were wrong were actually correct.

How did that help me. Well, at the time, my 5-year-old son was trying to learn how to ride a bicycle, I and he were totally frustrated because he just couldn't seem to get the knack of riding. His knees were so banged and scratched up that he wanted to quit trying to learn.

So.. I got to thinking, if one turns the hbars left to go right and vice-versa, and then reverses the operation when straightening up, this might help me to teach him to ride.

I told him, "When you are falling to the left, just steer the bike in the same left direction." I understood that this would force the tire patches back under the C/G and he would stop the fall. Now, admittedly, HE didn't know this principle, nor did I even try to explain it to him. So, simply telling him to steer toward the direction he was falling in was what I said to him.

We went out the next time, and VOILA, he took off riding and he never fell again.

I was so glad. I was getting tired of running alongside and seeing him wreck!!

 

[henzilla]

There also is the magic speed at which countersteering starts.Without searching, seems around 23mph was the consensus. What works at parking lot speed will not work above that threshold and vice versa

I learned more by riding and placing my chin over the hand of the intended direction I was headed...on bicycles and motors. Taking a downhill curve over 45MPH on a bicycle in control is a smile maker.

Reading how it works does nothing for me,but practicing it does. Have followed folks on every brand making six point turns in the slightest curve wears me out as well as preparing for them to fail. I will offer a tip in the kindest way to those who seem flummoxed and away from other riders...typically appreciated.

 

[pglaves]

There also is the magic speed at which countersteering starts.Without searching, seems around 23mph was the consensus. What works at parking lot speed will not work above that threshold and vice versa

I have ridden my F650 Dakar (single) through a series of switchbacks where it repeatedly switched back and forth between direct (tricycle type) and counter steering as the speed increased and decreased. Until I figured out what was happening it was scary.