need help with G29 FFB!

i recently got a G29 wheel for pc and i have a question about their FFB in common: I can feel the texture of the ground i am driving on when i do not steer left or right. As soon as i steer into a curve the FFB is mostly gone. I have this behaviour with FH4 and also other racing games. The strange thing is that if i use the Logitech SDK Demo to test out all the FFB effects i can steer much over 90° and the vibration effect is still very noticable. In the SDK Demo the center spring is completely off by the way…Is this norrmal for driving wheels?