"So ken, when you run, you start a right hand turn by taking a step to the left?"

You'll definitely initiate it with your left foot. It may not be a step to the left, but your foot is not directly under your center of gravity. That helps you lean, even when running you're not vertical when you turn. Being on the left foot hlps initiate your lean.

Consider an exaggerated case, a hard cut to the right that a football or basketball player might take. They do this by moving their left foot out very far from under themselves and can achieve a very aggressive lean and tighter turn. So in this case, they do turn right and initiate the turn by stepping left.

Wow, lots of deeper technical references here. I always thought about it in simple terms.

The rider is a big ball of mass that is elevated above the ground by a skinny pole (the bike) [Figure 1]. If I want the ball of mass to move to the left, I must be able to apply a force to the right on the ball, but I have no mechanism to apply a force to the ball at its side since the tires are way below the center of mass. In essence, the bike becomes a lever. I need to adjust the lever such that I can apply the force to the side. I do this by applying a force at the bottom of the lever in the opposite direction [Figure 2]. This puts the bike in a position like Figure 3. Notice that the bike is now applying force to the ball both up (to counter gravity) and to the left (the desired direction of travel). The left-right force can still only be affected at the contact point (the tires on the road), so if I want to remain off the ground, I need to turn either more rapidly or bring the bike back to upright. At this point, you are turning the handlebars in the direction of the turn, as you are trying to move the base of the lever back underneath the center of mass.

My "figures" are here since I don't know how to upload a picture to this site.


Oh well. I guess "its magic" really is the best explanation.

great. here's a test: can you explain that in more simple terms? ("gyroscopic "term" is a bit arcane)

Short of that, does the wheel/contact patch shape on the ground change when you lean over and does that effect the turning radius? To fully dumb it down ;-) ...if I slide a banana on its "rocker"/back it would likely travle straight, but if I slide it on its side, it might hook....

but if you are right up against to the curb, you can't turn away from it, you have to lean away from it...

If I want the ball of mass to move to the left, I must be able to apply a force to the right on the ball, but I have no mechanism to apply a force to the ball at its side since the tires are way below the center of mass. In essence, the bike becomes a lever. ...

Sure you do, just like a tricycle, you turn the handle bars

Just came across a page from your excellent (theoretical?) article http://socrates.berkeley.edu/...les/SteerBikeAJP.PDF , which reminded me to ask again, does the leaned-over sidewall change the tracking?

The picture of the motorcycle is the crux of my question: the rider is well into the turn; the bike is leaned over, the turn continues (as evidenced by the lean of the bike, situation of the bike at the apex, the direction of the rear wheel and the direction of the rider eyes) yet the front wheel is still pointing away from the direction of the bike's path (which you can see from both the angle of the tire and the rider's hands/bike handlebar).

If counter steer was only used to initiate a lean (to offset the centrifugal force of the turn and prevent the rider from toppling over), wouldn't the front wheel in the picture be angled into the direction of travel, instead of counter to it?

I take it you haven't done my ride through a puddle test and see how your wheels track when you turn after you leave the puddle. Just do the test.

I was watching an AMA flat track dirt bike race last weekend on TV (yeah, not much on) and noticed how really pronounced their countersteer was. More so than superbike racing - or bicycle riding, for that matter - I think because the turns are very tight and the front wheels of dirt bikes are more exposed (no faring, fender, etc) than on the street bikes. They're also fighting against sliding on the dirt towards the outside of the track - something we wouldn't do on a bicycle, but it really forced the riders to hang on to that countersteer until they were back on the straightaway.

You take it wrong on two counts, Art:

I did do your test: at low speeds you have to initiate with countersteer; at high speeds you can do it by leaning without counter steer...at least according to the tire track mark. Note the referenced article concurs that counter steering is not mandatory, "Countersteering and hip thrusts are two ways of creating the lean...")

But that isn't the question, which is: do you counter-steer all through the turn - modulate the turn via countersteer - because of the way the sidewall of the tire, when leaned over, causes the turn to be even sharper than you want.

Hence is the turn "balanced" out by both the body lean against centrifugal force tipping you over, and by the counter-steer to counter the fact that the sidewall of the tire, when leaned enough to counter the centrifugal force, would cause too sharp a turn....certainly the picture shows a motorcycle in the middle of a high speed turn, leaned over and still countersteering.

Check out any MotoGP pictures of bikes in the middle of the turns. Like the example in the cited paper, they all exhibit countersteer in the middle of the turn.

I can't answer those questions, but maybe those with real bike handling skills here can answer them.

I think I countersteer just for a moment, and then I lean the whole bike over. I am no hot shot bike handler though.

I think I countersteer at high speed as well, though it is brief. I think I can turn without countersteering, but it is tough and slow.

I never understood the sharp counter steers I see on the track. I wonder if you effectively get a braking action since the rear wheel slides sideways. It seems like that would tend to counter the centrifugal force and help you track around the curve.

If you think of a rock swinging around in a circle when held by a string, you realize that the force which causes it to move in a circle is the force which acts perpendicular to the direction of motion. In this case that comes from the string.

It is like gravity, it works everytime so it is not important. Just look at where you want to go and the bike follows. I don't think you have to understand physics to make it work. It is like throwing a ball. Pick ball up throw. Or spend your whole life trying to explain how the physics works. G

Your forte is econ and enduro....gravity works differently depending on where you are, countersteer should work all the time everywhere...maybe...I am just curious cause it is a wild concept! ;-)

I think it has to be so intuitive that no one could possible think it while doing it, at least at anything above real slow. It is one of those interesting things that everyone takes for granted, while doing it 1,000 a day (unless you are on the trainer ;-) and not knowing how it actually works. Yes, like gravity, G...sort of...but even my 7 year old has been taught about Isaac Newton sitting under a tree. (he was actually hit by a fig ;-)

Interesting discussion. Yes, countersteer is used to initiate a turn. Always. And it can be very subtle (as is the case with high speed turns). Hip lean? Interesting idea. But you can still move all over the bike and it won't stray froma straight line. I'll have to test that one some time (somehow).

But the act of countersteering is pushing the inside handlebar down farther into the turn, in essence leaning the bike over harder. It's the only way to change lines when in a turn. And you can probably lean that bike over much farther than you're comfortable with...

And it has everything to do with gyroscopic forces.

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it goes alittle something like this...... ;-)

"And it has everything to do with gyroscopic forces."

According to the two scientific references cited above, gyroscopic forces have very little to do with it.

Viking--that is beautiful! Do you get much static going to kids' playground all dressed in leather?

Well thank you everyone. I printed out this thread and followed the step-by-step instructions on "how to go around a corner". The good news is they say my bike can be repaired, and my shoulder should heal by April!