I don't think the gyroscopic affect is really the primary issue here. That has more to do with why the bike is STABLE rather than how to initiate a turn. Someone already answered this the way I see it, but maybe it seemed so simple that it just didn't sound right so I'll try to phrase it differently.

The PRIMARY reason this works is that when you turn the bars to the right, you obviously make the tires track off to the right, the bike's center of mass is then to the left of the tires and thus the bike leans (You basicallysteer the tires out from under the bike). Once leaning, the round profile of the tires means that the inside edge covers less ground per rotation than the outside edge and so you no longer travel straight, but rather turn. I probably said that badly. . . . The center of a rounded motorcycle tire has a larger diameter than the edges. When leaned over, one side of the tire is near an edge, the smaller diameter and the other side is near the center of the tire and its largest diameter. Roll a tireone revolutionlike this and both sides are travelling different distances, in other words it arcs rather than going straight.

That's my belief anyway. I'm not saying there aren't other factors, but without those other factors, you would still turn if you could lean a bike controllably. As I said earlier, the gyrosopic affect is more about stability. I doubt racing bicycles have run intoturning problems because their ultra-light wheels and tires have ruined their ability to gryoscopically turn their bikes. But I bet they are less stable than an amateurs bicycle partially due to that.

So leaning = turning and countersteering is just the quickest way to initiate the lean.

Kevin

 

92classic,
That's a good video of counter steering, that sums it up!

 

Awe crap . . . .
Now I have to THINK when I'm riding?


Excellent discussion. Now I have to go try it. My mind says no way but the explainations make sense. If I log in tomorrow with mega road rash, I'm gonna need to talk to some of you . . . .

Scott

 

Push left, turn left, yeah I remember that. It was invented by NASCAR!

 

It actually has everything to do with the gyroscopic effect of the turning wheels. If it didn't, then the phenomenon would work at any speed, or never at all. As it is, it only works above speeds of say, 10-15 mph as the wheels come up to speed and stability.

The idea is to get the vehicle to lean, and this is how ya do it. If you ever took a bicycle wheel or one of those toy gyroscopes, you'll see how difficult it is to turn the thing when it's spinng. It's actually easier to 'lean' the thing than to try to turn it.

If you've ever watched flat-track races,you'll see the phenomenon at it's most extreme.

 

Countersteering "works" at lower speeds too and I bet most of us subconsciously use it in parking lot maneuvers sometimes. If you tried it (without consciously affecting the lean in some other way), you would definitely find the bike would lean VERY quickly into a turn. Here are the main reasons we don't do it as much at low speeds: lack of stability so we tend to ride more upright atslower speedsand generally you want to turn much sharper at slower speeds than the tire profile alone will allow. Once you need to carve an arc tighter than yourtire profileallows, you also have to point the tire in the direction you want to go. Sometimes for really tight, slow speed turns you probably sometimes give it a flick to the opposite direction to starta lean and then steer into the turn. If you've ever done that in a parking lot,then youcountersteered at slow speed. You initiated a quick lean by steering the tires out from under the center of mass of the bike.

I agree the gryoscopic effect is part of the picture,I just don't think it'sthe primary reason countersteering creates a lean.

Kevin

 

Kevin it takes only a modest familiarity with a gyroscope to understand counter-steering - at least to understand how most people believe it starts to work. (They are generally WRONG, but I will explain their position nonetheless.) The phenomenon is called Gyroscopic Precession. This is what happens when a lateral force is applied to the axis of a spinning gyroscope. The spinning gyroscope translates the force vector ninety degrees off the direction of spin. Thus, if we try to turn our front wheel to the left, the force we use appears as a lateral force forward against the axle on the right side and this is translated into a force that tries to lean the wheel to the right. Similarly, trying to turn the wheel to the right results in the wheel trying to lean to the left.

But gyroscopic precession is not a necessary component of counter-steering. No matter how slight, if your front wheel deviates from a straight path your motorcycle will begin to lean in the opposite direction. It is entirely accurate to assume that even without gyroscopic precession, the act of steering the front wheel out from under the bike would start counter-steering in the opposite direction. This is a result of steering geometry - rake. You can observe it at a complete stop. Just turn your handlebars in one direction and you will see that your bike leans in the opposite direction as a result. [Please note that though gyroscopic precession is not a necessary component of counter-steering it facilitates it - makes it smoother - but does NOT cause it. In plain language - centrifugal force is what initiates counter-steering, not gyroscopics. Please see Centrifugal Force for a better understanding.]

In the case of a motorcycle, your handlebar input is immediately translated by gyroscopic precession into a lean in the opposite direction. Since your front wheel is attached to the bike's frame, the body of the bike also attempts to lean. It is the lean of the BIKE that overwhelms the handlebar effort and drags the front wheel over with it - gyroscopic precession merely starts the process and soon becomes inconsequential in the outcome.

 

What my instructor did a few years back was put the front wheel between his legs to lock it, and as I pushed the left or right bar, the bike would lean. This is a pretty good way to show how your bike will react while moving.

 

I noticed someone mentioned pushing down on the bars instead pushing forward. Pushing down on bars is basically the same thing as leaning the bike with your body to counter steer into a lean which is not the affective way of doing it as some of you know. You have to push FORWARD on the bars to have the bike really lean the bike into a turn most affectively.

 

I wasn't referring to the rake geometry either (though there's no doubt that also would contribute). I was just saying that it's my opinion that by FAR the biggest contributor to initiating a lean is the simple fact that the tires act on the bike at ground level. If you steer right, your tires will go right but your bike's inertia still takes the mass of the bike straight forward and then you are leaning, basically instantly.

I understand those other factors play a role, never disputed it, but with the incredible stabilizing affect of relatively heavy rotating engine parts, transmission gears and a typically larger rear tire, turning a skinny and lightweight 21" wheel/tire a mere tenth of a degree isn't going to torque the bike over in adramatic way. Rake geometry could shift thefront tire contact pointfrom the center of mass maybe an inch or less which would definitely cause a lean. But that's nothingcompared to shifting it by 6" in a similar period of time. A minor tweak of the handlebars, even at slow speeds will put your bike's center of mass WELL offline from the tires very quickly.

Kevin