| Why it Works! |
points it. A motorcycle changes lean angle when you steer it because it is balanced between gravity and lateral acceleration. When you steer it you vary lateral acceleration. Because it is laterally unstable lean angle change will occur with even the slightest change in lateral acceleration. |
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Motorcycles are NEVER laterally stable! A motorcycle is a motorized bicycle, if it is laterally stable it ceases to be a bicycle. If a motorcycle were laterally stable it would not counter steer it would turn like a car. No gyroscopic precession of any source on a bike resists lean angle change as a primary effect. That includes the front wheel. However, the reason that the front wheel generates resistance to lean angle change is that the precession of the front wheel (as a result of lean angle change and therefore a secondary effect) is transferred directly to the hands of the rider through the steering head. Any gyroscope that cannot move freely on a second axis is virtually irrelevant to the topic of lean angle resistance. Motorcycles do not become more stable the faster they go! Remember rule number one, motorcycles are never laterally stable. When you counter steer you are in fact trying to make the motorcycle fall over (partially). If a motorcycle is turned by the rider controlling the degree to which the machine is being leaned then resistance to changing lean angle cannot be defined as stability because it is resistance to control. Because there are only two wheels in tandem there is nothing that mechanically holds a bike in its lateral position. A rider uses this lack of lateral stability to balance and turn a bike with lateral acceleration via steering once forward motion begins. What is perceived as stability is really the gyroscopic precession of the front wheel resisting the rider's efforts. The gyroscopic precession of the front wheel actually counter steers the bike. (Precession steers the front wheel into the direction of lean angle change therefore effecting the amount of lateral acceleration, precession does not lean the bike nor does it hold it up.)That is why if you ghost ride a bicycle it does not immediately fall, it self corrects. Counter steering is the act of moving a bike's center of gravity in relation to the point that the bike touches the ground (changing lean angle). Because the front wheel is used to turn a bike it must be free to turn side to side. Because of this, when a motorcycle changes lean angle 100% of the precession of the front wheel must be resisted by the rider. The front tire alone weighs about eight pounds. The front wheel assembly including the rim, rotors and tire are around 24-26 pounds on a production sport bike. Therefore, in order to control a motorcycle you must over power a nearly 2 foot in diameter, 26 pound gyroscope that is doing up to 2700 rpm. If I want to work out I'll go to the gym. When the axis of a gyroscope is moved the resistance, or torque, is always generated at a 90 degree angle to the motion. This is why the front wheel is the source of dynamic resistance (it is generated only while lean angle is changing). Let me say it another way, all of the gyroscopic precession of the front wheel is transferred directly to the hands of the rider. If that resistance is canceled out then a motorcycle will steer almost effortlessly. In fact, we can adjust the resistance. |
am not saying that it is uncontrollable nor am I referring to a wobble. A bicycle by definition can never be mechanically balanced on the roll axis (laterally). If there is a third point holding it up it is then either a tripod or a tricycle. Tricycles do not lean in order to turn and therefore do not counter steer. Bicycles are controlled by moving the cg in relation to where the tires touch the ground. This is not true of any vehicle that has more than two wheels. Gravity acts on a bike vertically. Acceleration generated from steering input acts on a bike laterally at a 90 degree angle to gravity. Gravity remains constant. Lean angle varies the leverage that gravity has on a bike's cg. Lateral acceleration is variable via steering input. A rider uses steering input to achieve the amount of lateral acceleration required for a given situation. Lateral acceleration will change lean angle unless it is in equilibrium with the advantage that gravity has. For example, 45 degrees requires one g to hold a constant lean angle. If you are holding a static lean angle and then turn sharper to the inside of the turn, lateral acceleration will increase, overcome gravity and stand the bike up. Gravity is always pulling down with a constant force on a bike. When a bike's cg is balanced perfectly over its tires it goes in a straight line. If the cg is off to the side even slightly then lateral acceleration holds it up resulting in a radius that corresponds to lean angle and speed. When you are going in a straight line the increase in steering effort that comes with speed does give the perception of gyroscopic stability. That resistance to change that you are feeling is the precession of the front wheel. It is not holding the bike up, lateral acceleration does that. It is transferring torque at a 90 degree angle to the axis that it is rotated on. |
motorcycles or bikes work is knowing what is the action and what is the reaction. While a motorcycle's lean angle is in transition the front wheel generates precession. The act of changing lean angle is the cause of precession which if not resisted will steer the front wheel which then causes a change in lateral acceleration which changes lean angle which causes precession. Precession (specifically that of the front wheel) is an unnecessary evil. |