Bike Tilting: How Racers Produce Centripetal Force

[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.

 

[rcgldr]

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.

The assumption was the rider was already hanging off as much as possible before encountering the unexpected decreasing radius turn, so more weight can't be shifted over.

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)?

The bike leans right, the front tire turns right, and the rider leans left.

 

[berkeman]

The assumption was the rider was already hanging off as much as possible before encountering the unexpected decreasing radius turn, so more weight can't be shifted over.

Ah, no. For regular turns, even at reasonable speed (like offramps), you just end up with the middle of your butt on the inside edge of the seat. When I need to tighten up the turn, my butt slides more off the seat and down the inside of the bike some. For either countersteering or body steering, you'll only end up way down the side of the bike when you're pulling a high lateral force (like in racetrack turns).

Fred at Reg's CLASS school had a great line that he liked to use in the classroom sessions. He talked about trusting your tires, and how to handle getting into a turn hotter than you expected. He used to say, "Just lean more, just lean more." He was referring to putting more and more weight on the inside peg, pulling with the outside thigh, and getting lower and lower. It's definitely helped me a few times

 

[rcgldr]

He used to say, "Just lean more, just lean more." He was referring to putting more and more weight on the inside peg, pulling with the outside thigh, and getting lower and lower.

Except that putting more weight on the inside peg corresponds to the rider leaning outwards and now the turn is is no longer coordinated if no countersteering occured. Going back to your previous post, if you're standing on the ground, and you lift your left foot, you lean (fall) left. If you're standing on two scales, and you partially lift your left foot so the left scale shows less weight than the right scale (which now shows more weight), you also lean (fall) left.

 

[JeffKoch]

Did you watch the video of Reg at VIR? He uses body steering exclusively.

He most assuredly does *not*, even if he thinks he does and says he does. This is part of the problem with this topic, professional instructors tossing around terms like bodysteering and countersteering aren't being precise and are winding up misleading people. What he really means is that he's achieving a flowing style using his body and arms where he doesn't deliberately and consciously blast the bars with his arms, he does it smoothly and imperceptibly.