Countersteering works by moving the wheels out from under the bike.

Try this experiment: Balance a broom upside down on your finger. With a few minutes' practice you can keep it upright pretty effectively. Once it's reasonably stable, try moving it to the left. You'll quickly find that for the broom to move to the left, it must be leaning to the left. You do this by moving your finger to the *right*, which moves the end of the broom handle out from under the center of mass of the broom. This is exactly the same mechanism as countersteering. Your bike has some inherent stability when it's moving, which will tend to keep it upright. When you want to turn, you must lean the bike.

Countersteering moves the wheels out from under the center of mass of the bike, causing it to lean in the opposite direction. Gyroscopic precession has little bearing on countersteering. It does have a significant effect on the feel of the bike, since it tends to keep the front wheel from being turned. However, consider this: If gyroscopic precession were the primary driving force in leaning the bike, one would expect that bikes with large front wheels would turn in very quickly. As it turns out, though, this is not the case, and in fact is just the opposite of what is seen in actual practice.

Once the bike is leaned over, the trail of the front end causes the front wheel to turn into the curve, and the round profile of the tires causes the bike to experience camber thrust steering (similar to rolling a cone, which travels in a curved path), which cause the bike to go around the curve. When it's time to straighten out, countersteering is again used, this time to move the wheels back underneath the center of mass of the bike and cause it to stand up.

Clickfor full size image)

This an excellent graphic demonstrating what is happening. The key is that moving your butt moves the cg (y and x are the location in the image.) Basically what has to happen is for the moments created from the weight (mg) and the centrifugal force (mv^2/r) to cancel out. (A moment is a force times a distance, in this case the distance to the contact patch in the direction perpendicular to the force - mg*x for weight, (mv^2/r) * y for centrifugal force.) Then the bike goes around the corner and sparks fly from your titanium knee sliders. You can speed up and lean over (or drop your butt) until the centrifugal force equals the maximum force that the tires/road combination can handle. This is of course assuming that you're not doing anything else like braking or accelerating which takes away from the grip available for cornering. If you want the equations to play with: (mv^2/r) * y = mg * x -> m = mass, cancels out! It doesn't matter how fat your ass is for computing the speed/turn radius, just where it is and the ratio of ass fat to bike fat (it does matter for maximum speed though) -> v = velocity -> r = radius of turn -> y = vertical distance of cg from center of rotation (contact patch) -> g = acceleration due to gravity (constant 9.81 m/s^2) -> x = horizontal distance of cg from center of rotation The two forces are trying to rotate the bike in opposite directions which is why the are on opposite sides of the equation. so: v = square root(rgx/2y) OR r = 2yv^2/gx You can see that as y drops or x gets bigger (lean over more or hang off more for both, basically) either r has to go down (tighter turn) or v has to go up! Don't you just love physics?

Just for the record.....there is NO such thing as "centrifugal force" or any other "center fleeing force" for that matter.... The force acting on a body in uniform circular motion is referred to as the centripetal force, and is directed TOWARD the center of the circle. Force is force....the added word centripetal just means it points toward the center....;) Actually it is ANGULAR Accelleration that is at work to be specifically correct.

(Click here for full size plaque image.)


COUNTER STEERING - a longer version by James R. Davis - search down the list to find it