Bike Tilting: How Racers Produce Centripetal Force

[rcgldr]

What turns a bike is the angle between the direction the front and rear tires are pointed. If you vision extending the axis of the front and rear wheels, they will cross somewhere under the pavement (if the bike is leaning inwards). If you then note the point on the pavement directly above where the axis lines cross below, that will be the center of the circular path that the motorcycle would tend to follow for a given amount of steering input and lean angle, absent other forces.

Does it also depend on the forward angle of the forks and the distance between the extended line from the forks to the road and the contact point of the front tire with the road? In other words, is there a difference between a regular bike and a chopper in the amount you have to turn the wheel?

The fork angle and triple clamp placement affect trail, but not the turning radius, which is mostly a function of the steering angle and lean angle (tire width and profile have some effect). The trail is the distance from the imaginary extended steering axis to the ground back to the contact patch, which creates the tendency for the wheel to turn inwards when the frame is leaned to one side. More trail, like on a chopper, reduces the minimal speed for self correction, but it requires more effort to steer.

 

[A.T.]

Try this. With the help of a friend, walk your sportbike in a straight line, not holding the bars. It will probably track straight pretty well. Now lean the bike...

But what is that supposed to prove? The counter-steering is what leans the bike, when you ride it. When you walk side to side with it, you have obviously other means to lean it.

The experiment you would have to do is: Lock the front wheel, so it can steer only right. Ride it and try to make a right turn.

 

[rcgldr]

I know that the debate between countersteering and body steering is a bit contentious in general.

Not if you reduce the situation to just one wheel. I have never seen any unicycle article or rider that claimed that a unicycle rider could lean using any method other than counter steering. It's a uni-track vehicle, similar to balancing a broom upside down on your hand, if you want to move the broom left, you can't just move your hand left, you first have to move your hand right to get the broom to lean left so you can then accelerate it and move it left.

Body leaning on a bicycle or motorcycles only works because the steering geometry combined with the bike's reaction to body leaning (the bike initially leans outwards), results in a counter-steering response.

 

[berkeman]

It's hard to see but it's there, and this is why you turn without touching the bars at all. Very, very, very slowly. One way to get a feel for this is to experiment with how rapidly you move your butt off to the inside - if you blast off quickly, you turn more quickly, which supports the notion that the turning input is the blasting, not the weighting per se.

Body steering works no matter how slowly or rapidly you shift your weight. It's a smooth transition of weight to the inside peg that turns the bike in.

But what is that supposed to prove? The counter-steering is what leans the bike, when you ride it. When you walk side to side with it, you have obviously other means to lean it.

The experiment you would have to do is: Lock the front wheel, so it can steer only right. Ride it and try to make a right turn.

I don't want to do that experiment. I would crash if the front end cannot turn into support the turn radius.

Here's a variation of my suggested walking experiment that I think will eliminate your objection. Have a light friend stand on the footpegs as you and a buddy hold the bike up and walk it forward. Nobody touches the bars. As you are moving forward, have your standing buddy take their weight off of their left foot, and put all of their weight on the right footpeg. What happens to the bike? (It leans right) What happens to the handlebars? (They turn to the right without turning to the left at all).

 

[Andrew Mason]

For what it is worth, I rode a bicycle this morning and examined how I turned.

When I turned right going at a moderate speed, I instinctively turned the wheel to the left for a split second, leaned right and the wheel just seemed to turn right naturally. I could consciously avoid the countersteer to the left and just lean right and I could turn right but it seemed to be a little slower to get the bike to lean and turn.

When going downhill and braking while making a hairpin turn to the left (on a narrow ramp), I didn't countersteer before turning left because I could not lean the bike on the turn - my speed was too slow. It had to be very slow to make the turn.

AM

 

[cjl]

The experiment has been done. Specifically, a bike had a set duplicate handlebars mounted to it that was hard mounted to the frame, in addition to the regular set (so that the wheel was still free to turn, but the second set of handlebars was not connected to the wheel). Without the ability to countersteer, very little steering was possible, especially at speed.

http://www.superbikeschool.com/machinery/no-bs-machine.php

It may be completely unconscious, but if you are steering a motorcycle, you are countersteering.

 

[JeffKoch]

Body steering works no matter how slowly or rapidly you shift your weight. It's a smooth transition of weight to the inside peg that turns the bike in.

It does turn the bike in, and it does indeed turn much more rapidly if you blast off towards the inside quickly, but the turn rate is still slow unless you do one or both of two additional things: Roll off the throttle, or countersteer deliberately using the bars.

Some years ago I rode in a toys-for-tots ride, which was basically a parade ride at 25 mph led and followed by police escorts. I was riding a Ducati superbike and found myself very bored, so I put the throttle into fast-idle mode (acting as a cruise control at low speeds) and rode through the twisty canyon road with my arms flapping like a bird. Really. It worked fine, so it's not correct to say that you cannot turn without using the bars, and Code's bike also proves this. It is correct to say that you can only turn very gradually and at low speeds without using the bars or the throttle to help, and it is also correct to say that the act of leaning towards the inside forces the tire to go off-center towards the outside, which acts as a countersteering input.

It can't be any other way, that's just the physics of two-wheeled vehicles above a threshold speed where trials-riding tricks of weight shifts and balancing no longer work.

 

[rcgldr]

It can't be any other way, that's just the physics of two-wheeled vehicles above a threshold speed where trials-riding tricks of weight shifts and balancing no longer work.

Trials riders balance standing still bikes by generating torques as opposed to just weight shifts. One technique is to swing a free leg out and into help balance a bike. Also the amount of trail is greater, so steering inputs moves the front tire contact patch more side to side, allowing that to be used to help balance while standing still also. Another common method is to hop or bounce the bike while generating torques (or weight shifts if you want to call it that), that can be done to turn the bike while bouncing on the same spot.

A better example of this type of balancing would be high wire acts that use bicycles where the wheels ride on the cable and can't be steered. A "balance" pole is normally used that allows a lot of torque to be generated, but very skilled people can use their arms as balance poles, even though that only generates a relatively small amount of torque.

Some stunt videos show guys using the arm balancing and waist bending methods to ride motorcyles while standing on the seat. The bike's self-stability due to trail helps here. This is a stunt and the stunt guys sometimes crash, so I'm not suggesting anyone here try this.

 

[Andrew Mason]

... and it is also correct to say that the act of leaning towards the inside forces the tire to go off-center towards the outside, which acts as a countersteering input.

I'm am not sure I understand what you are saying. Are you saying that the front wheel would rotate to the right?

Let's look at angular momentum. By convention we use the right hand rule to determine the direction of the angular momentum vector. The angular momentum vector for the front wheel rolling forward is along the axle pointing horizontally to the left: call that \vec{L_i}.

If I lean left by shifting my centre of mass to the left of the centre of mass of the bike must shift to the right. This would tend to cause the axle, hence the angular momentum vector for the wheel, to move toward a position pointing above the horizontal (left): \vec{L_f}.

The change in angular momentum, therefore, would be a vector \Delta\vec{L} pointing vertically up (ie. \Delta \vec{L} = \vec{L_f }- \vec{L_i}). This \Delta\vec{L} corresponds to a torque on the front wheel about a vertical axis so that the front of the wheel would move to the left (ie. the front wheel would rotate in a counter-clockwise direction looking down at it).

This turning of the wheel results in a further change of the axle (hence angular momentum) direction. That change vector points backward horizontally and perpendicular to the axle. This means that there is a clockwise torque on the wheel looking from front to back which would tend to cause the wheel to lean to the left.

As soon as the front wheel starts turning to the left, the road puts a leftward lateral force on the front tire and causes the bike to turn left ie. in the direction the front wheel is rolling. This left turn changes the direction in which the axles point and, hence, the direction of the angular momentum vector. The change is again a vector pointing backward horizontally perpendicular to the axle, which means that there is further clockwise torque on the bike (looking front to back) ie. tending to cause the bike to lean further to the left. Of course, this torque is countered by the leftward lateral force of the road on the tires, which tends to rotate the bike to the right.

AM

 

[berkeman]

I'm am not sure I understand what you are saying. Are you saying that the front wheel would rotate to the right?

Let's look at angular momentum. By convention we use the right hand rule to determine the direction of the angular momentum vector. The angular momentum vector for the front wheel rolling forward is along the axle pointing horizontally to the left: call that \vec{L_i}.

If I lean left by shifting my centre of mass to the left of the centre of mass of the bike must shift to the right. This would tend to cause the axle, hence the angular momentum vector for the wheel, to move toward a position pointing above the horizontal (left): \vec{L_f}.

The change in angular momentum, therefore, would be a vector \Delta\vec{L} pointing vertically up (ie. \Delta \vec{L} = \vec{L_f }- \vec{L_i}). This \Delta\vec{L} corresponds to a torque on the front wheel about a vertical axis so that the front of the wheel would move to the left (ie. the front wheel would rotate in a counter-clockwise direction looking down at it).

This turning of the wheel results in a further change of the axle (hence angular momentum) direction. That change vector points backward horizontally and perpendicular to the axle. This means that there is a clockwise torque on the wheel looking from front to back which would tend to cause the wheel to lean to the left.

As soon as the front wheel starts turning to the left, the road puts a leftward lateral force on the front tire and causes the bike to turn left ie. in the direction the front wheel is rolling. This left turn changes the direction in which the axles point and, hence, the direction of the angular momentum vector. The change is again a vector pointing backward horizontally perpendicular to the axle, which means that there is further clockwise torque on the bike (looking front to back) ie. tending to cause the bike to lean further to the left. Of course, this torque is countered by the leftward lateral force of the road on the tires, which tends to rotate the bike to the right.

AM

Interesting. Thanks Andrew. I wondered why the bike seemed to steer itself based on the lean and balance.

 

[rcgldr]

Let's look at angular momentum. By convention we use the right hand rule to determine the direction of the angular momentum vector. The angular momentum vector for the front wheel rolling forward is along the axle pointing horizontally to the left: call that \vec{L_i}.

If I lean left by shifting my centre of mass to the left of the centre of mass of the bike must shift to the right.

When the bike shifts (rolls) to the right, that produces an angular momentum vector that points horizontally forward, and the sum of these two vectors, a long one pointed to the left plus a short one pointed forward, reflect the precession reaction of the front wheel, which will turn to the right.

The gyroscopic forces could be ignored on a two skate bicycle that uses curved blades instead of wheels (you'd have to push it with an external force, then ride it while it was gliding on the ice). The trail alone would result in a similar reaction, lean the bike to the right and the steering geometry results in the front blade turning right. This creates self stability and allows a rider to lean to the left, leaning the bike to the right, to cause the two skate bike to counter steer right during the initial response to the lean.

 

[Andrew Mason]

When the bike shifts (rolls) to the right, that produces an angular momentum vector that points horizontally forward.

Why? When I lean left and push the bike to the right, the net change in angular momentum of the bike about the horizontal would be 0, is it not?. There is no external torque if the centre of mass is over the wheels (so gravity is not supplying a torque) and if the road is not pushing laterally.

The only change in angular momentum that I can see is from the change in direction of the wheel axles which changes the direction of the angular momentum of the wheels and puts a clockwise or counter-clockwise torque on the wheels (looking down from above) depending on which direction the bike leans.

AM

 

[rcgldr]

When the bike shifts (rolls) to the right, that produces an angular momentum vector that points horizontally forward.

Why? When I lean left and push the bike to the right, the net change in angular momentum of the bike about the horizontal would be 0, is it not?

Ignoring the effect of contact patch forces in response to mass shifting to the side, angular momentum of bike and rider is zero, but this is the result of equal and opposing angular momentum vectors during the transition. Using right hand rule, while the rider leans left, the rider's angular momentum vector is horizontal and backwards, and while the bike leans right, the bike's angular momentum vector is horizontal and forwards, and the bikes angular momentum is what affects the front tire precession. The rear tire experiences the same effect, but in this case the precession reaction would be a slight yaw torque on the entire bike, in the same direction as the front tire's precession.

In addition, shifting the mass to one side results in a sideways force at the pavement, and because of the castor component effect of trail, this side force also tends to turn the front tire away from the movement of the rider. This would be easier to visualize if the moveable mass was relatively low, which would reduce the torque generated by sideways movements. The ratio of mass of rider versus bike also changes the effect of mass shifting, since the response to the generated torque is reduced by the angular inertia of the bike.

 

[JeffKoch]

I'm am not sure I understand what you are saying. Are you saying that the front wheel would rotate to the right?

YES. Try it with a bicycle tire in the garage. You moving off to the left, presumably wanting to turn left, means you are applying a torque on the right peg to lean the bike itself slightly to the right. This means the front wheel wants to turn to the right, which is the same thing as a countersteering push input on the left bar. The faster you blast off to the inside on the left, the more rapidly you'll turn, presumably because the opposite reaction on the bike is more rapid and allows the front wheel to turn more to the right before the bike starts to lean to the left.

 

[A.T.]

YES.You moving off to the left, presumably wanting to turn left, means you are applying a torque on the right peg to lean the bike itself slightly to the right. This means the front wheel wants to turn to the right, which is the same thing as a countersteering push input on the left bar.

Hand free countersteering is also described here:
http://en.wikipedia.org/wiki/Countersteering#No_hands

To turn left, a rider applies a momentary torque, either at the seat via the legs or in the torso that causes the bike itself to lean to the right, called counter lean by some authors.[3] The combined center of mass of the bike and rider is only lowered, of course. However, if the front of the bike is free to swivel about its steering axis, the lean to the right will cause it to steer to the right by some combination of gyroscopic precession (as mentioned above), ground reaction forces, gravitational force on an off-axis center of mass, or simply the inertia of an off-axis center of mass, depending on the exact geometry and mass distribution of the particular bike, and the amount of torque and the speed at which it is applied.[1][12]

This countersteering to the right causes the ground contact to move to the right of the center of mass, as the bike moves forward, thus generating a leftward lean. Finally the front end steers to the left and the bike enters the left turn.

 

[Andrew Mason]

I was just removing some change from my pocket and a penny fell out on the floor and rolled straight for a few feet before it began to lean over to the left. As it leaned left it began to turn left. It stayed leaning for some time as it rolled in a counter-clockwise (looking down) spiral path and then slowed down and fell over. I did not see it do a countersteer before it started turning. Did I miss something?

AM

 

[rcgldr]

a penny fell out on the floor and rolled straight for a few feet before it began to lean over to the left. I did not see it do a countersteer before it started turning.

In order for the penny to lean left, the contact patch must have been offset to the right of the center of mass, in order for the upward force from the ground at the contact patch and the downwards force of gravity at the center of mass to produce a torque that caused the penny to lean left.

Since the penny is similar to a unicycle, as mentioned before, I have never seen any unicycle article or rider that claimed that a unicycle rider could lean or smoothly turn (not hopping or twisting while stopped) by body leaning or using any method other than counter steering. Example unicycle forum thread:

http://www.unicyclist.com/forums/showthread.php?t=20698

 

[berkeman]

In order for the penny to lean left, the contact patch must have been offset to the right of the center of mass, in order for the upward force from the ground at the contact patch and the downwards force of gravity at the center of mass to produce a torque that caused the penny to lean left.

Since the penny is similar to a unicycle, as mentioned before, I have never seen any unicycle article or rider that claimed that a unicycle rider could lean or smoothly turn (not hopping or twisting while stopped) by body leaning or using any method other than counter steering. Example unicycle forum thread:

http://www.unicyclist.com/forums/showthread.php?t=20698

Maybe that is part of the disageement here. Just because the contact patches on a motorcycle move to the right to start a left turn, doesn't mean that the front wheel had to turn to the right to make that happen. I pull the contact patches on my sportbike to the outside all the time with my inside heel to initiate turns. No input to the bars, and the bars don't move until the front wheel turns itself into the turn. It's a smooth continuous motion, pull with the inside heel as you slide your butt to the inside and weight the inside peg.

 

[berkeman]

In order for the penny to lean left, the contact patch must have been offset to the right of the center of mass, in order for the upward force from the ground at the contact patch and the downwards force of gravity at the center of mass to produce a torque that caused the penny to lean left.

Since the penny is similar to a unicycle, as mentioned before, I have never seen any unicycle article or rider that claimed that a unicycle rider could lean or smoothly turn (not hopping or twisting while stopped) by body leaning or using any method other than counter steering. Example unicycle forum thread:

http://www.unicyclist.com/forums/showthread.php?t=20698

Maybe that is part of the disageement here. Just because the contact patches on a motorcycle move to the right to start a left turn, doesn't mean that the front wheel had to turn to the right to make that happen. I pull the contact patches on my sportbike to the outside all the time with my inside heel to initiate turns. No input to the bars, and the bars don't move until the front wheel turns itself into the turn. It's a smooth continuous motion, pull with the inside heel as you slide your butt to the inside and weight the inside peg.

 

[rcgldr]

In order for the penny to lean left, the contact patch must have been offset to the right of the center of mass, in order for the upward force from the ground at the contact patch and the downwards force of gravity at the center of mass to produce a torque that caused the penny to lean left.

Maybe that is part of the disageement here. Just because the contact patches on a motorcycle move to the right to start a left turn, doesn't mean that the front wheel had to turn to the right to make that happen.

I only mentioned that the contact patch had to move to the right, not how it was moved. If the rider leans left, the bike leans right, and if the rider prevent the front tire from steering outwards, perhaps camber thrust from the slight outwards lean is enough to move the contact patches outwards. Another possibility is deformation at the contact patches, but the lateral force generate by weight shifting doesn't seem like it would cause signficant deformation.

Deliberate countersteering (applying outwards torque on the handlebars) is going to result in a much faster response than body leaning, based on my own experience, and almost every article I read about counter steering.

 

[berkeman]

I only mentioned that the contact patch had to move to the right, not how it was moved. If the rider leans left, the bike leans right, and if the rider prevent the front tire from steering outwards, perhaps camber thrust from the slight outwards lean is enough to move the contact patches outwards. Another possibility is deformation at the contact patches, but the lateral force generate by weight shifting doesn't seem like it would cause signficant deformation.

Deliberate countersteering (applying outwards torque on the handlebars) is going to result in a much faster response than body leaning, based on my own experience, and almost every article I read about counter steering.

I disagree on the first part, and agree with you on the second part.

If the rider leans left, the bike leans right,

You don't "lean" in bodysteering, you shift your weight. When I shift my body weight to the left to turn the bike into the left, the bike most certainly does not lean to the right.

Deliberate countersteering (applying outwards torque on the handlebars) is going to result in a much faster response than body leaning, based on my own experience,

I would mostly agree with this, but even on a racetrack, you don't usually need much faster transitions than you can generate with aggressive body steering. The exception is chicanes, where you do a left/right or right/left transition as fast as you can. Body steering is plenty fast for the Corkscrew at Laguna Seca, for example.

Did you watch the Pridmore VIR video that I linked to? He seems to be doing just fine on his racetrack transitions...

And again, the reason I don't like to use countersteering is that it loses effectiveness in emergency situations, and gets folks away from staying balanced on the footpegs in turns (where you can get surprixed by traction issues). That's one of the important lessons we can learn from riding MX and dirtbikes -- there's a reason that you should carry your weight on the footpegs.

 

[JeffKoch]

When I shift my body weight to the left to turn the bike into the left, the bike most certainly does not lean to the right.

Most certainly it does lean to the right, initially. The front tire follows, turning to the right, which leads to the bike now leaning to the left and the front tire following. It may not seem to happen this way, but it does happen this way. And I guarantee that if you try the corkscrew on Code's bodysteering-only (actually bodysteering and throttle steering only) bike at more than about 15 mph, you will be sampling the Monterey dirt.

 

[berkeman]

Most certainly it does lean to the right, initially. The front tire follows, turning to the right, which leads to the bike now leaning to the left and the front tire following. It may not seem to happen this way, but it does happen this way. And I guarantee that if you try the corkscrew on Code's bodysteering-only (actually bodysteering and throttle steering only) bike at more than about 15 mph, you will be sampling the Monterey dirt.

No, sorry. I'm not an idiot, I know when the bars move, and they definitely do not move out when I turn in at any speed. I don't hold onto the bars generally, keeping open hands for controls only, but I would feel if the bars yawed opposite during turn-in. There is no homeopathy here boys.

Before anybody else suggests that the front end turns out during body steering, they need to do the experiment that I suggested many posts ago. Two supporting folks walking the bike, and one lighter "rider" who shifts their weight from both pegs to one. QED.

Keith's "No BS" bike is a good test, IMO. I always wished that Reg or Jason would challenge Keith on the bike, but that never happened. I think it's because the No BS Bike limits your small corrections at speed, but I could be wrong about that. I think I'll check out Keith's website, and maybe ask for a free ride on the No BS Bike to check it out.

BTW, if any of y'all are in NorCal, it would be good to ride with you two-up behind me. If you are light enough, I can show you for sure about how the front wheel (doesn't) move (out) during Body Steering.


EDIT / Add -- And again, the main reason that I'm okay with debating this is becaue relying on countersteering can get you killed. Not good. Learning to body steer has saved my bacon several times on the street. There's a reason that we balance on the footpegs in MX...

 

[rcgldr]

body steer

Other than being an indirect form of counter steering, I've never heard an explantion how weight shifting can cause a bike to lean in the same direction as the weight shift. Is there an explanation for how the bottom pendulum in what is essentially an inverted double pendulum ends up leaning in the same direction as the upper pendulum when the upper pendulum shifts its weight "inwards"?

Also in what situation would it be risky to use countersteering as opposed to body leaning?

 

[JeffKoch]

No, sorry. I'm not an idiot, I know when the bars move, and they definitely do not move out when I turn in at any speed. I don't hold onto the bars generally, keeping open hands for controls only, but I would feel if the bars yawed opposite during turn-in. There is no homeopathy here boys...

No, there's just physics. Try holding a bicycle wheel by the axle, spinning it in the forward direction as if your arms were directed down and the axle ends are the pegs, then push down on the right peg - the front wheel turns right. This is just the gyroscopic component, there are other aspects to the physics of turning a bike, but it's enough to give you the correct sense of what happens. You push on the right peg to lean to the left, so there's your effective countersteering input.

If this does not suffice, Tony Foale has an excellent engineering-level textbook on the whole process, it's an interesting read. The wiki article posted above is also interesting, though of course it's Wiki so not a proper reference.

It's easy to fool yourself riding a motorcycle, thinking certain actions cause certain reactions and missing other actions and reactions that are really responsible. You're far from the first person who misses the critical initial slight right turn of the front wheel that occurs when you lean to the left and want to turn left.

BTW I think Keith probably still remember me as the only person who was ever able to ride his no-BS bike, from like 10 years ago. You can ride it, but most people don't spend enough time and effort to figure it out - using the throttle is critical to doing more than barge-like arcs and crashing repeatedly. There are no tricks, he's just added a fixed set of bars that are attached to the frame, and added a second throttle - I forget if there are two brakes, but I don't think there are. You launch off with the usual set of bars, get up to desired speed, then quickly swap your hands up the second set of bars and continue without being able to turn the bars with your arms.

 

[berkeman]

Also in what situation would it be risky to use countersteering as opposed to body leaning?

There are two situations where I've had trouble with countersteering. Perhaps others don't experience these issues, but I've seen enough folks crash so I think they are common problems.

The first is something I've mentioned earlier in the thread. When you get into an emergency situation (get into a decreasing radius turn too hot, or have cars cut in front of you requiring a hard swerve and braking, etc.), it's natural for your arms to tense some. But since countersteering requires you to use your arms to turn, the tensing impedes your ability to turn well. With body steering, you basically move your body to tighten up the turn radius, or jump to the side to swerve quickly. For me at least, I can body steer in scary situations, where I would not be able to effectively countersteer. And since I believe in the addage, "Train like you fight and fight like you train", I try to never use countersteering if possible, so I won't be tempted to try it in an emergency situation.

The second issue has to do with balance on the bike in turns. For those of you who ride MX or dirtbikes, you know how important it is to keep the majority of your weight on the footpegs, and not up on the seat or tank. This is so the bike can be moving all around underneath you (in pitch and yaw axes), and your body weight does not affect the bike. You are decoupled from the bike's movement, so you are in control without getting thrown around. On a streetbike, when you get into an unexpected slide or skip in a turn, it's best to be balanced on the pegs with 20% or less of your body weight on the seat. That let's the bike move and recover on its own, with minimal control input from you. There have been times when I've hit mud or gravel in the dark in turns, and have been able to ride it out bacause I was balanced on the pegs when it happened.

Anyway, if countersteering works for you in emergency situations, then more power to you. Ride safe and smart folks.

 

[rcgldr]

There are two situations where I've had trouble with countersteering. ... The first is something I've mentioned earlier in the thread. When you get into an emergency situation (get into a decreasing radius turn too hot, or have cars cut in front of you requiring a hard swerve and braking, etc.), it's natural for your arms to tense some. But since countersteering requires you to use your arms to turn, the tensing impedes your ability to turn well. With body steering, you basically move your body to tighten up the turn radius, or jump to the side to swerve quickly.

In the case of an unexpected decreasing radius turn, if you've already body steered to lean into the original turn, and you're now hanging off the inside of the bike in a turn, how do you "body steer" any further in order to increase the lean angle?

I have a 2001 Suzuki Hayabusa, I'm already applying some amount of outwards torque on the handlebars to to maintain a lean angle (otherwise it tries to straighten up, depedning on the speed). On my bike, the front tire is steering inwards, but I use some outwards torque so it steers less inwards than the steering geomety would otherwise tend to do on it's own. If I need more lean angle I just increase the outwards torque on the handle bars, or vice versa, it's almost instinctive now. Most of my weight is on the seat and handlebars, not the pegs.

For those of you who ride MX or dirtbikes.

MX or dirtbikes have a lot of trail. Keith Code readily admits his dirt bikes can be easily steered by body leaning, or weigh shifting with most of the weight on the pegs. It's the 600 cc road racer replica no bs bike with a small amount of trail that is difficult to lean by body steering, without playing games with the throttle (that could be indicating some swing arm play if throttle is affecting cornering response).

Getting back to road racing bikes as speeds increase, they tend to be less responsive to body leaning or weight shifting due to gyroscopic forces resisting any lean angle change without a lot of counter-steering torque applied to the handlebars. At 100 + mph => 160 + kph, the response rate to body leaning or weight shifting is so slow that it's almost imperceptible. The tendency to straighten up on my bike also goes away, it's neutral and just tends to hold a lean angle until I apply considerable countersteering torque on the handlebars , and the amount of counter steering effort to straighten up is about the same as it is to lean over.

Back to sport bikes in general, I find I can ride them similar to classic Formula 1 racers, keeping my body in the middle and tucked in behind the windscreen, so my body is motionless relative to the bike, only using countersteering inputs to change lean angle. I can also hang off like current motorcycle racers. One method I don't understand is some of them now swing one leg outwards during corner approach.

 

[berkeman]

In the case of an unexpected decreasing radius turn, if you've already body steered to lean into the original turn, and you're now hanging off the inside of the bike in a turn, how do you "body steer" any further in order to increase the lean angle?

You just keep shifting more weight over and farther down. I use this all the time in decreasing radius turns, or if I need to tighten my turn line up suddenly.

Getting back to road racing bikes as speeds increase, they tend to be less responsive to body leaning or weight shifting due to gyroscopic forces resisting any lean angle change without a lot of counter-steering torque applied to the handlebars. At 100 + mph => 160 + kph, the response rate to body leaning or weight shifting is so slow that it's almost imperceptible.

Did you watch the video of Reg at VIR? He uses body steering exclusively. And I've done plenty of turning at a buck plus at racetrack track days, using only body steering. I acknowledged earlier in the thread that you can transition quicker using both body steering and countersteering, but unless it's a very quick chicane, the extra transition speed isn't really necessary, IMO.

One method I don't understand is some of them now swing one leg outwards during corner approach.

I remember watching Rossi do that a few years back. Either he mentioned that it was just to relax him, or that's the impression I got by watching him. It's one of the few places on a track you could stretch out a bit.

 

[berkeman]

Other than being an indirect form of counter steering, I've never heard an explantion how weight shifting can cause a bike to lean in the same direction as the weight shift.

It seems to just be the torque of the weight shift on the pegs.

I tried a simple experiment on my ride back from the workout pool today. It's similar to what I was suggesting as an experiment earlier in the thread, but you can do it all by yourself.

(Don't do this in an obvious place on the public roads, BTW... and don't try this if you think you may crash as a result.)

Ride standing and leaning forward just enough so that you can keep a light touch on the bars to hold a steady throttle, with your weight balanced on both pegs. Keep your knees out a bit, so there is no contact with the tank, seat or side panels. Now lift your left foot off the peg, transfering all of your weight to the right peg. What happens? Which way does the bike lean, and what do the bars do (and not do)?

 

[Allenman]

As a mechanic I can tell you that the reason tilting the bike while not holding the handlebars allows you to make a turn is due to the caster angle of the steering arm. If the steering fork is perpendicular to the road surface, you will not turn at all when you lean the bike. The smaller the angle of the steering fork relative to the roadway (think chopper) the more the wheel will turn when the bike is leaned either direction. Too little angle and the steering will become super sensitive and the wheel will flop sideways when you lean.