Motorcycle physics -- Countersteering and Bodysteering

[Erunanethiel]

I didn't want to delete or edit the original thread, since it had a lot of information in it but due to me not being specific enough when asking the question, we got non specific answers. I tried to reach the moderators in the other thread about opening a new thread but could not succeed, hopefully this won't bother them. So here goes:

On a frictionless road and tires, I know the rider wouldn't be able to change the combined center of gravity of the system by moving his weight around. If he pushes the bike to lean to the right, he would go to the left by the amount that would keep the combined cog the same. But a bike with real tires and a real road under it is not a closed system, the tires wouldn't let the lower part of the bike left or right when trying to initiate lean. Does this mean it is possible to push with your bodies inertia to the bike, and the combined cog will be changed?

I think if you do so below the center of mass of the bike, you could, but I am not sure, since the tires will want to move more, but won't be able to, making the combined center of gravity shift more than if you applied the force higher up. And I think you should use horizontal forces on the pegs not up/down forces on the pegsI know counter steering is the best way, but I would like to think it is possible to change direction without it, without the influence of handlebars

Please ignore gyroscopic forces and assume the bike doesn't have any trail geometry (so you would have to "catch" the bike manually through the handlebars)

Thank you very much

 

[berkeman]

Thread closed for Moderation...

 

[berkeman]

Okay, thread will be re-opened (now in the ME forum), with the focus on countersteering and bodysteering a motorcycle. Here is the previous thread for reference:

https://www.physicsforums.com/threads/motorcycle-physics-question.926581/

I tried to reach the moderators in the other thread about opening a new thread but could not succeed, hopefully this won't bother them.

Next time, please just click the "Report" link on your post to ask for the help of the Mentors/Moderators.

Does this mean it is possible to push with your bodies inertia to the bike, and the combined cog will be changed?

Yes, as mentioned in your previous thread, using shifted weight on the footpegs and seat will lean the motorcycle over to start a turn.

I know counter steering is the best way, but I would like to think it is possible to change direction without it, without the influence of handlebars

Countersteering is a pretty reliable way to initiate a turn on a motorcycle, but it has a couple of practical problems that bodysteering addresses.

First, countersteering relies on you being able to use your arms to push-pull the handlebars to move the front tire contact patch to one side to initiate a turn in the other direction. The problem is that in emergency situations on the road, your arms tend to tense up and your ability to countersteer around an obstacle goes way down. That panics you even more, which makes your arms tense up even more, and you can guess what happens next. This is one of the common reasons that new motorcycle riders often fail to make it around a turn or a highway onramp/offramp -- they tense up, straighten up, and ride right off the outside of the turn. Bad news.

The other problem with countersteering is that even if you are very, very good at it (I used to be), it is very hard to have the precise control in a hard turn or turn combination that you would like. I learned bodysteering at Reg Pridmore's CLASS schools, and the first few times I tried to ride down the Corkscrew at Laguna Seca, I kept missing the best fall line, and was wide at entry, or in transition between the two turns, or at exit. It was very frustrating. But I finally started listening to Reg more in the classroom portion of the school, and heard him talking about bodysteering and letting the bike steer itself with the front end once you used your weight shift to start the turn. I started using that through the Corkscrew and the other turns at Laguna Seca, and what a difference! The bike really did just steer itself down the fall line once you used your weight shift to get it turned in the right overall direction at the start of the turns. Amazing.

I don't know if it was covered in your previous thread, but Keith Code (who runs a competing motorcycle racetrack school) has build a "No BS" (no bodysteering) sportbike, where you can take your hands off of the handlebars and still control the throttle, front brake and clutch from a fixed set of bars on the bike. Apparently riding it is pretty scary, since you have lost your normal low-speed control of the bike. I'm guessing that Reg or his son Jason would have no problems riding the No BS bike at speed around tracks, but I haven't asked him about it.

Also, I think you asked about a fixed front fork arrangement in your previous thread. That won't work for steering the bike. In bodysteering, you need the bike's geometry to be able to turn the forks into the turn and track the natural balance through the turn.

Hope that helps. Thread is now re-opened.

BTW, here is the Corkscrew -- one of the most fun places on Earth!

https://image.redbull.com/rbcom/010...oing-through-the-corkscrew-at-laguna-seca.jpg

 

[rcgldr]

Somewhat related - a bit of history regarding hanging off on a motorcycle.

https://www.cycleworld.com/2014/08/...ing-styles-part-one-of-three-by-kevin-cameron

https://www.cycleworld.com/2014/08/...ing-styles-part-two-of-three-by-kevin-cameron

https://www.cycleworld.com/2014/08/...g-styles-part-three-of-three-by-kevin-cameron

 

[rcgldr]

Back on to counter-steering, a videos of a no bs bike. Although some have claimed that Keith Code stated that body-steering doesn't work, Keith only stated that it's not as as fast or effective as direct counter steering as explained in the video. At 1:35 into the first video, the rider has difficulty weight shifting to chang the lean angle to the other side. In my opinion, the rider didn't shift enough of his weight to fully change the lean angle, but on a narrow 2 lane road, couldn't risk experimenting with more radical movement.



Here is a video of the original "no bs" bike. It appears that it was setup (perhaps deliberately) so that it was almost impervious to body-steering. Extreme body shifting only results in mild lean responses from this version of the "no bs" bike. The bike's setup would not noticeably affect it's response to counter-steering. The bike can be seen at 2:15 into this video. At 3:35 into the video, a pointer connected to the handlebars of a normal bike to show the handle bar movement.

 

[Erunanethiel]

Okay, thread will be re-opened (now in the ME forum), with the focus on countersteering and bodysteering a motorcycle. Here is the previous thread for reference:

https://www.physicsforums.com/threads/motorcycle-physics-question.926581/Next time, please just click the "Report" link on your post to ask for the help of the Mentors/Moderators. [emoji2]Yes, as mentioned in your previous thread, using shifted weight on the footpegs and seat will lean the motorcycle over to start a turn.

Countersteering is a pretty reliable way to initiate a turn on a motorcycle, but it has a couple of practical problems that bodysteering addresses.

First, countersteering relies on you being able to use your arms to push-pull the handlebars to move the front tire contact patch to one side to initiate a turn in the other direction. The problem is that in emergency situations on the road, your arms tend to tense up and your ability to countersteer around an obstacle goes way down. That panics you even more, which makes your arms tense up even more, and you can guess what happens next. This is one of the common reasons that new motorcycle riders often fail to make it around a turn or a highway onramp/offramp -- they tense up, straighten up, and ride right off the outside of the turn. Bad news.

The other problem with countersteering is that even if you are very, very good at it (I used to be), it is very hard to have the precise control in a hard turn or turn combination that you would like. I learned bodysteering at Reg Pridmore's CLASS schools, and the first few times I tried to ride down the Corkscrew at Laguna Seca, I kept missing the best fall line, and was wide at entry, or in transition between the two turns, or at exit. It was very frustrating. But I finally started listening to Reg more in the classroom portion of the school, and heard him talking about bodysteering and letting the bike steer itself with the front end once you used your weight shift to start the turn. I started using that through the Corkscrew and the other turns at Laguna Seca, and what a difference! The bike really did just steer itself down the fall line once you used your weight shift to get it turned in the right overall direction at the start of the turns. Amazing.

I don't know if it was covered in your previous thread, but Keith Code (who runs a competing motorcycle racetrack school) has build a "No BS" (no bodysteering) sportbike, where you can take your hands off of the handlebars and still control the throttle, front brake and clutch from a fixed set of bars on the bike. Apparently riding it is pretty scary, since you have lost your normal low-speed control of the bike. I'm guessing that Reg or his son Jason would have no problems riding the No BS bike at speed around tracks, but I haven't asked him about it.

Also, I think you asked about a fixed front fork arrangement in your previous thread. That won't work for steering the bike. In bodysteering, you need the bike's geometry to be able to turn the forks into the turn and track the natural balance through the turn.

Hope that helps. Thread is now re-opened.

BTW, here is the Corkscrew -- one of the most fun places on Earth! [emoji3]

https://image.redbull.com/rbcom/010...oing-through-the-corkscrew-at-laguna-seca.jpg
View attachment 212609

How about if you use weight shifting on a bike with no trail in it's geometry?

That was the I meant to ask actually in the first thread when I said "locked steering", I actually meant "no trail" as I actually learned how trail worked.

Does the act of leaning to one side on the motorcycle (and the motorcycle leaning the other way) cause a change of lean angle due to tires resistance due to friction with the road to not let the motorcycle's lower part move, without trail in the bike's geometry?

An easier way to ask the same question is this:

When the rider leans right on the motorcycle with no trail (looking from behind), does the motorcycles lean to the left cancel the rider's movement completely, keeping the combined center of gravity the same? If no, which way would the system fall to, if you didn't "catch" the fall with countersteering "manually"?

And does where and how you apply the force make a difference?

Thank you very much for keeping the thread open, I will do as you say if I ever need to contact moderators or mentors

 

[berkeman]

When the rider leans right on the motorcycle with no trail (looking from behind), does the motorcycles lean to the left cancel the rider's movement completely, keeping the combined center of gravity the same?

I don't know what happens with no trail. I do know that the rake and trail of modern sportbikes is virtually the same among different brands, because over the years they have been able to optimize them at the track.

As for the weight shift in bodysteering, you generally have most of your weight on the footpegs during cornering, and to turn in you pull with your inside heel and weight the inside peg and unweight the outside peg. This folds the front end in as the bike and you lean over. You end up leaning more than the bike, with the center of your butt typically along the inside edge of the seat. Stay balanced on the pegs (heavier weight on the inside one).

 

[rcgldr]

Does the act of leaning to one side on the motorcycle (and the motorcycle leaning the other way) cause a change of lean angle due to tires resistance due to friction with the road to not let the motorcycle's lower part move, without trail in the bike's geometry?

Simplify the situation to the rider only applying a lateral force at some point above the bike's center of mass. The variables are the bikes angular momentum compared to it's mass, how far from the center of mass to the bottom of the tires, and how far from the center of mass to where the rider applies a lateral force to the bike.

Note that the forces between ride and bike are Newton third law pairs. You could consider this as the rider pushing against the bike and the bike pushing against the rider (the rider's leg muscles are pushing in both directions).

How the bike reacts depends on the variables. If absent friction, the bike would "lean" more than it translates, then with friction, the pavement pushes in the same direction as the rider pushes on the bike, and the center of mass of the system moves towards the bike's direction. If absent friction, the bike would "lean" less than it translates, then with friction, the pavement pushes in the same direction as the bike pushes on the rider, and the center of mass of the system moves towards the rider's direction.

 

[Erunanethiel]

Simplify the situation to the rider only applying a lateral force at some point above the bike's center of mass. The variables are the bikes angular momentum compared to it's mass, how far from the center of mass to the bottom of the tires, and how far from the center of mass to where the rider applies a lateral force to the bike.

Note that the forces between ride and bike are Newton third law pairs. You could consider this as the rider pushing against the bike and the bike pushing against the rider (the rider's leg muscles are pushing in both directions).

How the bike reacts depends on the variables. If absent friction, the bike would "lean" more than it translates, then with friction, the pavement pushes in the same direction as the rider pushes on the bike, and the center of mass of the system moves towards the bike's direction. If absent friction, the bike would "lean" less than it translates, then with friction, the pavement pushes in the same direction as the bike pushes on the rider, and the center of mass of the system moves towards the rider's direction.

The amount the bike translates is not inversely correlated to how much it leans though, how much it will translate is always dictated by the impulse, no matter how far away you pushed from the center of mass and how much "spin" or "lean" you initiate. There is a video about it that veritasium tries it, but can't explain it well enough, so I actually got the answer from this forum, which made me sign up here. The answer is that work≠impulse, so even if impulse is the same, you can do more work by pushing off the center off mass so you push for "longer" so that explains where the extra kinetic energy of spin comes from, the impulse is the same so the block reaches the same height vertically

This is the video:

 

[rcgldr]

The amount the bike translates is not inversely correlated to how much it leans though

The amount that the center of mass that the bike translates is related to the impulse, but the amount that the contact patches of the tires would translate on a frictionless road would depend on the variables I mentioned in my last post.

Consider a long rod of in space, and an impulse applied to one end of the rod, perpendicular to the rod's orientation. If the rod's angular momentum is low enough (a rod with uniform mass distribution would have low enough angular momentum), then although the rod's center of mass moves in response to the impulse, the other end of the rod initially moves in the opposite direction as the impulse.

 

[Erunanethiel]

Simplify the situation to the rider only applying a lateral force at some point above the bike's center of mass. The variables are the bikes angular momentum compared to it's mass, how far from the center of mass to the bottom of the tires, and how far from the center of mass to where the rider applies a lateral force to the bike.

Note that the forces between ride and bike are Newton third law pairs. You could consider this as the rider pushing against the bike and the bike pushing against the rider (the rider's leg muscles are pushing in both directions).

How the bike reacts depends on the variables. If absent friction, the bike would "lean" more than it translates, then with friction, the pavement pushes in the same direction as the rider pushes on the bike, and the center of mass of the system moves towards the bike's direction. If absent friction, the bike would "lean" less than it translates, then with friction, the pavement pushes in the same direction as the bike pushes on the rider, and the center of mass of the system moves towards the rider's direction.

Is it possible to apply a lateral force to the bike preferably low down on the bike like pegs in order to make the most of the friction stopping the tires move laterally, so the center of mass would shift more to the side the rider leaned in to?

 

[berkeman]

Is it possible to apply a lateral force to the bike preferably low down on the bike like pegs in order to make the most of the friction stopping the tires move laterally, so the center of mass would shift more to the side the rider leaned in to?

That sounds like what I was describing in post #7, although the pulling force with the inside heel is more to pull your body weight over to add weight to the inside footpeg to fold the bike into the turn. It may do something to push the tire patches to the outside, but I haven't felt that as a primary affect of the pulling motion.

 

[rcgldr]

Is it possible to apply a lateral force to the bike preferably low down on the bike like pegs in order to make the most of the friction stopping the tires move laterally, so the center of mass would shift more to the side the rider leaned in to?

The rider would have use his own angular momentum as resistance to any lateral force applied that doesn't go through the riders center of mass.

Consider the scenario where the rider applies a lateral force at the pegs (assuming the pegs are close to or below the bikes center of mass), and zero force at any other point on the bike. This will cause the rider to rotate about the roll axis due to the force that the pegs exert onto the riders feet as part of a Newton third law pair of forces. The pegs are so far below the riders center of mass that the rider could not generate much force, especially compared to the total weight of the bike + rider, but it would result in the force from the pavement be in the opposite direction of the force the rider applied to the pegs.

So for example, the rider exerts a force to the left on the pegs, and the pegs exert a force to the right onto the riders feet. In this case the pavement exerts a force to the right on the tires, so the center of mass of bike and rider move to the right, but the rider is leaning to the left (the "wrong" way).

The rider could exert internal torques on the system of bike and rider by leaning at the waist, or better still by swinging a free leg outwards, which is what trials riders do when stationary, in addition to taking advantage of caster offset with steering inputs and hoping the bike off and on the ground to maintain balance and/or reorient the bike. Trials bikes are relatively light, and leg swinging may not do much for a heavier street bike.

A bike on a tight wire is a good analogy for a bike with locked steering. The tight wire bikes are light, and a long and fairly heavy balance pole is used to generate the torques needed to balance the system.

 

[Erunanethiel]

So for example, the rider exerts a force to the left on the pegs, and the pegs exert a force to the right onto the riders feet. In this case the pavement exerts a force to the right on the tires, so the center of mass of bike and rider move to the right, but the rider is leaning to the left (the "wrong" way).

In the previous posts we came to the conclusion that the systems center of mass would shift to the side where the rider leaned in to, and I can't fathom out what is different this time

 

[rcgldr]

In the previous posts we came to the conclusion that the systems center of mass would shift to the side where the rider leaned in to, and I can't fathom out what is different this time

Previously, I only considered a lateral force close to or below the bikes center of mass. If the lateral force is applied high enough above the bikes center of mass and the bottom of the tires are low enough below the bikes center of mass, then the tires would want to move the other way, and the force from the pavement would be in the opposite direction of the rider's movement relative to the bike.

 

[Erunanethiel]

Previously, I only considered a lateral force close to or below the bikes center of mass. If the lateral force is applied high enough above the bikes center of mass and the bottom of the tires are low enough below the bikes center of mass, then the tires would want to move the other way, and the force from the pavement would be in the opposite direction of the rider's movement relative to the bike.

Okay, I see

In the usual case the pegs are likely to be below the center of mass of the bike, I think. In that case;

In order to apply horizontal forces through the pegs, you have to push the other way first right? Or you would end up rotating the opposite way you want to rotate and the bike rotates the other way, from what I understand. Am I correct?

 

[berkeman]

In order to apply horizontal forces through the pegs, you have to push the other way first right? Or you would end up rotating the opposite way you want to rotate and the bike rotates the other way, from what I understand. Am I correct?

As for the weight shift in bodysteering, you generally have most of your weight on the footpegs during cornering, and to turn in you pull with your inside heel and weight the inside peg and unweight the outside peg. This folds the front end in as the bike and you lean over. You end up leaning more than the bike, with the center of your butt typically along the inside edge of the seat.

What country/state are you in? Is there beginner motorcycle riding instruction available where you live? It sounds like you would gain a lot by getting out and doing some riding...

San Jose CMSP training -- https://www.pacificmotorcycletraining.com/

General CMSP California program -- http://2wheelsafety.com/register/

Overall Info -- https://www.msf-usa.org/BRC.aspx

 

[Erunanethiel]

What country/state are you in? Is there beginner motorcycle riding instruction available where you live? It sounds like you would gain a lot by getting out and doing some riding... [emoji2]

San Jose CMSP training -- https://www.pacificmotorcycletraining.com/

General CMSP California program -- http://2wheelsafety.com/register/

Overall Info -- https://www.msf-usa.org/BRC.aspx

I do not live in the USA, and I do ride, I have a Ducati 1098 currently.

But the theory of it still confuses me, and I can't try many things in this thread because my bike has trail in it's geometry and very expensive parts that need to be replaced in case of an accident [emoji23]

 

[berkeman]

Ducati 1098

Sweet!

http://images.mcn.bauercdn.com/PageFiles/487776/Ducati_1098-Photo.jpg

 

[rcgldr]

In the usual case the pegs are likely to be below the center of mass of the bike, I think. In that case;
In order to apply horizontal forces through the pegs, you have to push the other way first right? Or you would end up rotating the opposite way you want to rotate and the bike rotates the other way, from what I understand. Am I correct?

From my prior posts:

Consider the scenario where the rider applies a lateral force at the pegs (assuming the pegs are close to or below the bikes center of mass), and zero force at any other point on the bike. This will cause the rider to rotate about the roll axis due to the force that the pegs exert onto the riders feet as part of a Newton third law pair of forces. The pegs are so far below the riders center of mass that the rider could not generate much force, especially compared to the total weight of the bike + rider, but it would result in the force from the pavement be in the opposite direction of the force the rider applied to the pegs

... and the rider leaning the wrong way.

 

[Erunanethiel]

That's not what I meant

If I want to lean right (looking from behind) and I applied a force to the left, my body would rotate to the left (and the bike to the right).

So if I want to lean to the right, I need to push a bit to left first, like if you want to move a broom balanced on your hand to the right, you need to move your hand a bit to the left initially, so you can move it to the right without it tipping over

 

[Erunanethiel]

Sweet!

http://images.mcn.bauercdn.com/PageFiles/487776/Ducati_1098-Photo.jpg
View attachment 212891

Thank you!

 

[rcgldr]

That's not what I meant

If I want to lean right (looking from behind) and I applied a force to the left, my body would rotate to the left (and the bike to the right).

So if I want to lean to the right, I need to push a bit to left first, like if you want to move a broom balanced on your hand to the right, you need to move your hand a bit to the left initially, so you can move it to the right without it tipping over

If you apply a left force on the pegs, you end up leaning left and the right force from the pavement moves the center of mass of the system to the right, and the combined force applied to pegs and tires leans the bike left. With the steering locked, I don't know if the tire contact patches end up under the center of mass or offset to one side or the other.

 

[Erunanethiel]

If you apply a left force on the pegs, you end up leaning left and the right force from the pavement moves the center of mass of the system to the right, and the combined force applied to pegs and tires leans the bike left. With the steering locked, I don't know if the tire contact patches end up under the center of mass or offset to one side or the other.

If the rider stands up on the pegs and pushes to the left on the pegs, doesn't he lean to the right? Isn't that the case when we walk too?

 

[rcgldr]

If the rider stands up on the pegs and pushes to the left on the pegs, doesn't he lean to the right? Isn't that the case when we walk too?

You can try this while standing on your left foot. If you push to the left, your upper body leans to the left (or you can raise your right leg), and fall to the right until you correct the imbalance.

 

[berkeman]

If the rider stands up on the pegs and pushes to the left on the pegs, doesn't he lean to the right? Isn't that the case when we walk too?

You can try this while standing on your left foot. If you push to the left, your upper body leans to the left (or you can raise your right leg), and fall to the right until you correct the imbalance.

The footpegs are not flat ground. As you unweight your right foot and transfer that weight to your left foot, the bike folds over to the left. Think standing on a short see-saw with your feet straddling the middle fulcrum. If you lift one foot, your body drops down...

 

[rcgldr]

The footpegs are not flat ground. As you unweight your right foot and transfer that weight to your left foot, the bike folds over to the left. Think standing on a short see-saw with your feet straddling the middle fulcrum. If you lift one foot, your body drops down...

The OP was asking what happens when you exert a left horizontal force on the pegs, not a downwards force on the left peg, or a differential vertical force on the pegs. The goal here is to exert a left force onto the pegs, and in turn, have the tires exert a left force onto the pavement, so that the pavement exerts a right force onto the tires, in turn causing the center of mass of bike and rider to be accelerated to the right, in a locked steering scenario.

 

[Erunanethiel]

You can try this while standing on your left foot. If you push to the left, your upper body leans to the left (or you can raise your right leg), and fall to the right until you correct the imbalance.

I am confused

 

[Erunanethiel]

What is the answer we came up with to the original question?

 

[rcgldr]

What is the answer we came up with to the original question?

For the locked steering scenario, if the rider applies a lateral force too high above the center of mass, and the tire contact patches are too far below the center of mass, then the Newton third law pair of forces between tires and pavement are in the "wrong" directions.

If the rider applies a lateral force at the pegs, the Newton third law pair of forces between tires and pavement are in the "right" directions, but the rider ends up leaning the "wrong" way, except if the rider raises a leg to do all of the "leaning". Only a small amount of lateral force can be applied in this manner.

Body leaning or weight shifting to turn requires the indirect counter-steering reaction of the bike when it's initially leaned to the "outside" in response to the rider leaning to the "inside", in order to steer the tires to the "outside" to setup the lean of the system of bike and rider for a turn.