If the problem you are having is over sensitivity of steering, try this:
Since you have a 180 deg wheel and the in game cars have higher degrees of rotation, your wheel movements will be exaggerated in the game.
You can try this, set your "wheel turn" in Options->Control to say "120" degrees. Then set wheel turn compensation to "1". Then you will get some linearity in the first 120 degrees of turning, but after that it will accelerate and max out the in game sterring when you hit your 180 deg lock.
The only other way to get absolute 1:1: linearity through out the rotations is to get a wheel with say 720 / 900 degrees of rotation.