How to calculate force needed to turn a rack and pinion steering wheel

[Reddy]

How to calculate the forcee needed to turn steering wheel in a rack and pinion steering system ??

 

[Baluncore]

The force will be determined by tyre pressure, tyre contact with the road, the vehicle speed and the rate of change of direction.
There will be a mechanical advantage ratio proportional to (pinion radius) / (steering arm length * steering wheel radius).