Rotation speed increase gradually

Hi, basically the car rotates or 'tilts' around the center as controlled by the player, but because of the script i use it is very sudden, ie there is no 'easing' into or out of the rotation, I was wondering what i could use to create this easing so when the player presses the input key the rotation speeds up until a certain point, then when they let go it slows down quickly, but not suddenly as it is doing.

 function FixedUpdate () {
 //query input axes if necessarry
 if(queryUserInput)
 {
     brake = Mathf.Clamp01(-Input.GetAxis("Vertical"));
     handbrake = Input.GetButton("Jump")?1.0:0.0;
     //steer = Input.GetAxis("Horizontal");
      motor = Mathf.Clamp01(Input.GetAxis("Vertical"));
  }
 else
 {
     motor = 0;
     //steer = 0;
     brake = 0;
     handbrake = 0;
 }

if (Input.GetAxis("TiltLeft")){ transform.Rotate(Vector3(-1,0,0));

  }

if (Input.GetAxis("TiltRight")){ transform.Rotate(Vector3(1,0,0));

  }

}

It is the last part that controls the rotation, obviously :P