Calculation of steering wheel radius

1. Bone Attribute (Default)

If a custom attribute "steering_wheel_radius" or just "radius" exists on the "steering_wheel" bone, radius is taken from its value.

2. Stub Based Calculation

Else if there's a helper bone "steering_wheel_stub", the radius is computed from its distance to the steering_wheel bone Y-axis.

3. Mesh Based Calculation

Otherwise the radius is computed from the bounding box of mesh(es) attached to the steering bone.