Defining a coordinate system with origin at blue point (mount) and axes X (Reach), Y (Width), and Z (Stack), torque moment \(\vec{\tau}\) is the vector product between position vector \(\vec{r} = (R, W/2, S)\)and impulse force vector \(\vec{F} = (0, -I, 0)\):

$$\vec{\tau} = \vec{r} \times \vec{F} = (S \cdot I, 0, -R \cdot I)$$

This vector has two non-zero components with fundamental physical meaning:

• \(\tau_x = S \cdot I\) (Roll/Lean Moment): This is the torque acting on the bicycle’s longitudinal axis. It is the torque the rider exploits to lean the bike and corner at high speeds (lean steering).
• \(\tau_z = -R \cdot I\) (Horizontal Bending Moment): The Reach parameter generating it is directly linked to passive stability.