# [Physics] Effect of position on a motorbike turning

forcesfree-body-diagramnewtonian-mechanicsspeed

While searching tips for driving a motorbike on wet roads safely, I heard some pilots saying to lean inside the slope makes the bike less tilted, so it's safer.

I agree leaning make the bike less tilted, but the overall "motorbike+pilot" object isn't less tilted. The bike is less tilted because the pilot is more.

Here my drawing of the two situations :

a. is normal position
b. is tilted position
green crosses are centers of gravity of 'motorbike+pilot'

For a. and b. :
– same speed
– same mass, so same weight
– same angle from blue line (line from contact point to the canter of gravity of 'motorbike/pilot') to the floor
– same centripetal force
– vectors (in red) are the same

On my bike (Yamaha TW) tires are perfectly rounded, so the surface in contact with the floor is the same whether or not it's tilted. So I don't see a difference.

Am I wrong somewhere ?
How can it be safer ?

It is mainly about the so-called "effective steering angle" which is a function of the tilt angle and not necessarily equal to the steering angle measured at the handle bars.

The sensibility of the tilt angle with regard to the steering is much higher at high tilt angles. This is because the sensibilty of the effective steering angle with regard to the steering is higher at high tilt angles. This means that the bike is easier to control, or less sensible, at lower tilt angles.

Although the total center of mass is in both pictures tilted equally, in the picture b) the tilt angle of the bike is lower and thus the rider can control the bike by steering more easily.