While rolling or static ?
Why don't you simply measure it ? Strap a lever of a known length onto the steering wheel and pull on the lever with a fish scale. And the measurement you need to operate the stock steering will be
Torque, because the
Force will vary with the length of the lever.
Don't want to discourage you one bit, but if you don't know how to make basic force measurements, then how are you ever going to complete such a project ?