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Leaning/Turning are NOT Equivalent
Push Right - GO Right

By: James R. Davis

I think I have not made a compelling case for recognizing that leaning and turning are NOT synonymous.

Counter-steering is used to change direction only. It is NOT used to change lean angle. 'Push Right - GO Right' is correct. 'Push Right - Lean Right' is not and perhaps more importantly, 'Lean Right - GO Right' is not either.

This is especially troubling to me as it relates to people who are convinced that BODY lean angle can be used to steer a moving motorcycle - especially, again, bicycle riders. When you lean your BODY right the motorcycle MUST lean to the left! (It is how you lift a dragging peg off the ground, after all.) If your mind is convinced that leaning (your body) away from a potential accident is the way to avoid that accident you end up with the tragedy of my lady friend who did just that and (combined with target fixation) caused her to steer right into a head-on with a car and nearly cost her her left leg.

If leaning (both your body and the bike) invariably means turning then how can you explain how you handle crosswinds - the bike/body lean into the wind while the bike continues in a straight line if you simply counter-steer that straight line.

THROW AWAY the concept that leaning causes a change of direction!!! A change of direction changes the lean. More correctly, turning causes centrifugal force which, in turn causes leaning. Leaning does not cause centrifugal force, without which no turning is occurring.

Let's see if this makes the concepts clearer. Here is a diagram that on the left shows a motorcycle that is about to drag a peg in a turn and on the right it shows what happens if the motorcyclist leans INTO the turn. (It lifts the peg off the ground.)



The solid black line is the lean angle of the combined motorcycle and rider in that turn. Note that that line remains EXACTLY where it was when the rider leans in one direction while the bike itself leans in the opposite direction. The motorcycle maintains exactly the same course through that turn despite being leaned farther away from its apex and the same would be true if the rider had leaned away from the turn resulting in the motorcycle leaning farther into it.

The speed and radius of the turn establishes the lean angle of that black line! You CANNOT change the direction of travel by changing the lean angle but if you change the direction of the turn, the lean angle will change.

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http://www.msgroup.org

(James R. Davis is a recognized expert witness in the fields of Motorcycle Safety/Dynamics.)

     
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