Motorcycle Turning, Part 1 - Physics

I'm nowhere near a veteran, but infact I'm very much a newbie. But I hope to share what I've experienced, read, learnt and felt about riding. Following is a series of tech speak compiling from various instructors, column writers, famous authors and personal experience. Hope it helps you.

Gravity Defying
A common rider would usually perceive motorcycle steering in speeds of ~25km/h and above unnecessary. Because the gyroscopic and inertia force of the moving motorcycle would lock the steering bar in a straight and forward-going manner. Any form of turning or cornering at that kind of speed would require a shift in weight, which is usually performed by the banking/leaning/tilting the machine chassis to create a counter force against the forward motion, commonly known as Centrifugal Force.

The common myth is that, any movement on the handle bar during high speeds would result in a unpredicted haywire wobbling and movement of the motorcycle. Thus most of us would just lean as required when cornering. But it's nothing more than just a mystery. How many of you really understand how a motorcycle really turns?

Considering the fact that the front wheel doesn't really move at higher speed cornering, what makes a motorcycle move in a circular motion when leaning? 2 main factors, the shape of your tires and your directional front wheel.

Upright Tire
As depicted from the picture above, the contact point of the tire is always flat. This is due to the acting of the motorcycle's weight on the tire, flattening the contact side of rubber. This flat surface hence create a larger contact patch and allow better traction.

Banking tire forms a conical shape
However, when the tire is leaned to the side, the flat surface occurs over the contact patch as well. The occurance immediately results in a circumference differential between the inner and outer tire. This phenomenon thus creates the physical properties similar to that of a cone. In which, it allows the inner tire which has a greater circumference (in yellow) to travel further on the difference of the smaller outer circumference (in red). And therefore, the motorcycle which is travelling on convex tires can corner/turn just by banking.

Ofcourse, another main reason which allows motorcycle to turn is the front wheel which controls the direction of the moving chassis. Though you may not realise it, but the fact is that the handle bars are off-center and turning towards the direction when cornering. Because of the fast moving speed, the adjustment of the front wheel is limited according to the reaction of the banking angle reacting to the centrifugal force. Thus the movement of the handle bar is not noticeable.