Countersteering/Steering torques (was: How do I measure rake?)

[Mark McM]

Maybe we should have another go at this. The topic drifted from the original thread, so its probably best to start another thread.

I never experienced a self-steering condition, ever.

Actually, I think you have experienced a force that can cause self-steering, even if you did not recognized it as such. I'll try to keep this short and simple, but please first bear with me in this prelimary example:

The principle of action/reaction is important for all mechanical devices. Described by Newton's 2nd Law, it often expressed as "Every action has an equal and opposite reaction". A simple example would be if you are on tug-of-war team pulling on the left end of a rope, opposing another team pulling on the right end. If your team pulls harder, the rope moves to the left. If the other team pulls harder, the rope moves to the right. But if both teams pull equally (and opposite), the rope doesn't move at all. What if the rope passed through a hole in a wall, and you couldn't see the other end of the rope? If you are pulling the rope toward the left but the rope isn't moving, then from the action/reaction principle you know that even though you can't see the other end of the rope, you know that someone (or something) is pulling equally in the opposite direction. Pretty obvious, right?

Now on to steering a bicycle. As you know, if you push forward on the right end of the handlebar, it turns the front wheel to the left, and if you push forward on the left end of the bar, it turns the front wheel to the right. Say that you are leaned over into a steady-state constant radius right turn. To stay in this turn, the wheel has to remain pointed at an angle to the right. You have previously said that to stay in a right turn, you have to push forward on the right end of the bar to maintain a constant countersteering force. But this countersteering force is trying to turn the front wheel to the left. So if the front wheel doesn't turn left and remains pointing to the right, then from the action/reaction principle, we know that there must be an equal and opposite force pushing the wheel to the right. This means that for a constant radius turn with an applied countersteering force, there must also exist an equal and opposite steering force (such as an inherent "self-steering" force). Until you can wrap your head around this this, it is difficult to understand how a bike's steering mechanism works.


Just as a test, I have completed high speed right hand corners on my bicycle, using only my right hand, with an open palm, so it was not possible to pull on the bars or push on the left side to bring the bike out of a turn. All I did was push to turn and quit pushing to quit turning. I make a special effort to make my right turns only with my right hand and left turns with my left hand.

You should repeat this test, but this time after settling into the turn, try adjusting your lateral hip angle outward while keeping the turn radius the same; in other words, bend laterally at the hip so that your upper body is leaned a little bit more into the turn, and your lower body (and the bike) are leaned over a bit less. You should notice that the amount of countersteering force on the inside handlebar decreases. If you adjust the hip angle enough, you can make the countersteering force go to zero. Keep angling your hips outward even further, and the handlebar forces will reverse, and you'll have to pull back on the inside handlebar to keep it in the turn. Conversely, if you angle your hips more inward toward to the turn you'll find that required countersteering force will go up.


I also say that there is no body English or special body position required to make an effective turn at high speed. Just don't forget to keep the inside pedal up. While it may be possible to turn a bike in some other manner, it's not going to enhance cornering precision or get the bike around a corner any faster.

This I agree with. But different body positions can change the 'feel' of the steering, and can influence the rapidity and forces of of turn initiation and exit.

[Dave]

Sorry Mark, but I'm done with this subject. I didn't even bother to read very much of the stuff you posted before and I'm not going to read much of what you just posted. I know how to successfully steer a bike and need no science to convince me that it works.

I should not have disagreed about the possibility of a bike or motorcycle turning without any countersteering torque, but in reality, it's not common, mainly due to the fact that the bike's speed would have to remain absolutely constant and the desired turning radius would have to be a fixed. A curve in the road rarely has a fixed radius to follow. Even a small change in speed will affect the turning radius and require some input to correct the bike's path. I often ride on roads that have been sanded and I have to keep the bike in a very narrow patch of clean pavement, following car tracks. That path would not have a fixed radius and my speed is never constant. I always accelerate out of a high speed turn, on bike or motorcycle. The result is constant tweaks to the steering. It's entirely possible that the bike steers itself for a second or two, but it's not obvious to me.

About all the explanation I can give for the bike righting itself is increased speed, at the end of the turn. I absolutely do not use both hands in a push pull fashion to negotiate a turn and I don't alternately push and pull on one side of the bars either. I proved that to myself by riding through high speed corners, using only one hand with an open palm. I also don't do any type of leaning to the side or weighting of the outside pedal, to steer the bike. I try to keep the process as simple as possible.

I've read some pretty silly instructions from people who think you need to adjust your hip and shoulder position, lean a certain way, push down on top of the outside bar or outside pedal (so the bike won't fall over!). All a bunch of baloney.

I read about one line of your suggestion about adjusting my "lateral hip angle outward" and quit there. The force required to steer a bike is so small and the turn takes such a short time, that you'd never "feel" anything.

Lets just say you're absolutely right and I don't have a clue. Works for me.

[forrestw]

Here's a couple of things I think I learned on motorcycles that may apply in some small way to bicycles.

First, whether steering is perfectly neutral or normally requires continued countersteer is for me rather a moot point: If I'm executing a turn at anything like best speed I'm paying a whole lot of attention to the road ahead and what the machine is doing as I move through the turn and I'm paying far more attention to the effect of steering input than whether my net steering input is neg, pos or neutral. My approach to steering is minimalist, keeping upper body and grip on the bars relaxed, allowing the steering to initially absorb changes in road surface, correcting after as needed rather than trying to keep it rigid. I also keep the outer leg close to locked as that helps connect body to bike frame, not unlike gripping a motorcycle tank with knees/thighs.

(Lately I've been amused to find that cornering fast on rough pavement on a fixed gear setup is a whole other experience and it's interesting to be becoming accustomed to feeling the rear wheel lifting off the ground as I can't adapt as well to bumps as I can freewheeling.)

Second, something I learned the hard way on a motorcycle, if your bike is leaned over more or less all the way *and* you're hanging off to get the min possible turn-radius then if you lose traction you've got damned few options left for recovery, about the only one is rolling on some power to increase the power/traction and that will often require more space / road than you've got to play with.

Conversely, if you lean your body out a bit away from the axis of the turn, while putting the bike relatively close to it's max lean angle and you lose traction, recovery is actually quite simple: reverse your counter-steer, this will rotate the bike up to a lower lean angle, you can keep the entire system in balance by leaning your body lower (so bike and body pivot at your butt). As the bike rotates up, its mass bears harder on the road surface (you're lifting say 400 lbs of bike say 2" higher in the space of a fraction of a second) and this will cause your sliding rear wheel to regain traction. I don't think this will work well on a bicycle, haven't tried :-).

[Mark McM]

I read about one line of your suggestion about adjusting my "lateral hip angle outward" and quit there. The force required to steer a bike is so small and the turn takes such a short time, that you'd never "feel" anything.

Lets just say you're absolutely right and I don't have a clue. Works for me.

The suggestion of trying different hip angles was just as an experiment, I didn't mean to suggest that it was necessary, or even recommended, for standard cornering technique (although I'm still sure that it is possible to feel something).

And in the first sentences in my last paragraph I basically agreed that in the big picture, we're both right.

[RPS]

1) Torque is torque and is not defined solely by direction of force:

Because the fork and front wheel rotate about the centerline of the head tube on bearings to form the steering axis, a normal bicycle reacts to torque applied to the fork’s steerer tube the same whether one pushes on the right, pulls on the left, or a combination of the two. It may be easier to teach a rider to push but that’s not the only way to get the same steering effect. The bicycle doesn’t care at all how this torque is supplied as long as it is the same. Just observe riders with only one (functional) arm. They can steer in both directions (right and left) just fine by both pulling and pushing on the bars.

2) In reality there is no such thing as steady state when steering a bicycle:

Whether riding a straight line or on a turn, a bicycle is always in the process of falling over unless the rider uses “continuous” steering inputs to balance it. If at any time -- whether going straight or turning -- the steering axis was locked the bike and rider would fall over very quickly (almost instantenously). A rider can not set up a truly steady state condition any more than a pencil will balance itself on its point. With great smoothness a rider can APPROACH a “steady state” condition making it seem he is not steering but that’s not actually the case. A rider must always steer a bike on a continuous basis by either turning the bars, leaning to create a steering torque (like when riding hands off bar), or a combination of the two.


Based on above, I don’t understand emphasis on “self steering” attributes when clearly they can’t keep a bike upright without continuous rider input. And on the subject of countersteering, someone should define what they mean because I see it used to describe two very different things. That ambiguity causes confusion IMHO.

[Dave]

I can't remember reading of more than one definition of countersteering. To me it means applying force to the bars that would turn the wheel in the opposite direction of the turn. As I've said far too many times, I push forward on the right side (like turning left) to lean the bike to the right and turn right. IMO, motorcycle instructors emphasize this to keep the process simple. More advanced techniques are useful for racing, but have little value on the street.

Some discussions get bogged down in analyzing the exact angle of the wheel. IMO, that does not matter, you just need to know to push harder to tighten a turn or less to increase the turn radius.

When I'm descending a mountain road, I try to do most of my braking ahead of a turn, which means that the bike is constantly accelerating through the turn, even without pedaling (since I'm going downhill). That creates the need to constantly fight the tendency to swing wider as the speed goes up. A bike won't self-steer at a fixed radius if it's accelerating.

[Mark McM]

Based on above, I don’t understand emphasis on “self steering” attributes when clearly they can’t keep a bike upright without continuous rider input. And on the subject of countersteering, someone should define what they mean because I see it used to describe two very different things. That ambiguity causes confusion IMHO.

Yes, "self steering" can not keep a bike upright all by itself, but it makes it a lot easier for the rider to do it. "Self steering" is the entire basis for stability in a bicycle. It helps keep the bike stable not just in turns, but even when going straight ahead. How? As you said - a bike is constantly in the process of falling over, and the rider has to continuously add steering inputs to correct for imbalances. Self steering gives the bike the inherent ability to turn the front wheel into the direction that it is "falling over", helping the rider to balance the bike. The self steering not only reduces the rider's inputs, but can also begin to act before the rider even becomes aware that they are starting to fall over, and also acts to slow down the "fall" once it starts.

One of the main purposes of trail in bike steering geometry is to provide this self steering tendency. Trail causes the front wheel to want to turn in the direction of lean, which provides a self-steering torque to help re-balance the bicycle. This is why bikes with more trail tend to feel more stable - they have a greater self steering tendency. Contrary to what some might think, trail does not make a bike stable by keeping the wheel pointed straight ahead; as you point out, if the front wheel was always kept dead straight ahead, the bike would fall over. If the trail acted to keep the wheel pointed straight ahead, the rider would have to fight this tendency when adding steering to correct for imbalances, which could the bike feel more unstable not less. Instead, a bike with more trail tends to needs less corrective input on the handlebars - because the mechanism of the trail is that the bike automatically provide part of the steering correction for you. This ability for trail to add stability (due to self steering) happens both when riding straight ahead, and when turning.

David Jones wrote an interesting article about his attempt to build an unrideable bicycle, by attempting to eliminate the self-stabilizing mechanisms inherent in the bike. He never did make a completely unrideable bike, but he did make a nearly unrideable bike by introducing negative steering trail. Here's the article.

The stability of the bicycle (http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf)

[RPS]

I can't remember reading of more than one definition of countersteering. To me it means applying force to the bars that would turn the wheel in the opposite direction of the turn. As I've said far too many times, I push forward on the right side (like turning left) to lean the bike to the right and turn right. IMO, motorcycle instructors emphasize this to keep the process simple. More advanced techniques are useful for racing, but have little value on the street.

Some discussions get bogged down in analyzing the exact angle of the wheel. IMO, that does not matter, you just need to know to push harder to tighten a turn or less to increase the turn radius.
Dave, I’ll assume this is in reply to my post above so I’ll respond.

The common or normal definition of “countersteering” I’m familiar with is in the context of an “initial and momentary” turn left to enable the rider’s body to start falling to the right in order to get the correct lean angle necessary to make a right turn; after which time the front wheel is “essentially” pointed in the direction of travel (by whatever torque is necessary). Unless a rider is sliding around a turn the bike can’t have the front wheel pointed left while turning right other than to set up the initial lean.

I personally don’t like to refer to a steering torque to the left in order to maintain the front wheel pointed right as countersteering. This is what I interpret many of your comments to suggest in the form of definition – a counter steering torque rather than a counter steering angle. I can see how it can be used that way but I think it causes confusion. Rather I refer to the direction the front wheel is pointed and not the direction of steering torque I’m contributing.

By the way, since all bikes don't react equally to steering input, your suggestion may not work the same on my bike (I'm almost certain it wouldn't).

[RPS]

Instead, a bike with more trail tends to needs less corrective input on the handlebars - because the mechanism of the trail is that the bike automatically provide part of the steering correction for you. This ability for trail to add stability (due to self steering) happens both when riding straight ahead, and when turning.
I get what you are saying but have to think about the "mechanism" by which it happens. Is it truly "self steering" as you describe it or more like it magnifies the weight transfer of the rider to a greater degree so as to make balancing by continuous countersteering easier? ;)

Either way the result is the same so it really doesn't matter much. Personally I prefer a bike with much less trail than most.

[shiftyfixedgear]

It is awful early in the year, but this post (and other similiar ones) easily wins the award for most boring, confused, and pointless exercise in misusing supposed Physics ideas to try and describe what happens when someone tries to steer a bike.

What a waste of bandwidth.

[Charles M]

Fwiw,,,

Buy kieth codes book on road motorcycle handling:twist of the wrist...


Pretty much all of it applies to road bikes as well, it's just that with the vastly different weights involved, the handling sensitivity is 100 times higher.

There is counter steering in cycling. There is self steering. There is the resistance to leaning and turning from the centrifugal force of wheels...


It's loads easier to understand those forces at speed while pushing a performance moto in handling... You have to put serious weight and muscle in to it. Virtually all apply to cycling including body position to keep max tire contact, weighting the outside pedal to lower cog and counter steering to change your line.


You have to really push to make any of this have a real difference or benefit, and at some point, virtually all levels of rider have experienced it. But feel and understanding in those situations is a big variable...


Just 2 cents...