Mein Force Feedback wird beim fahren immer schwächer. Ist das normal?

It is not uncommon for the Force Feedback to weaken during driving, especially in higher power output settings - a phenomenon commonly known as "head fade." Generally, electronics and electric motors tend to become less efficient as (operating) temperatures increase, affecting all electromechanical systems, including Force Feedback wheels.

Fanatec is aware of this design/performance challenge and invests significantly in both software and hardware development to optimize this behavior and ensure a consistent output of torque and speed.

While earlier models could show a subtle performance loss that some customers noticed, the current Wheel Bases have been optimized to such an extent that performance loss over extended periods, even at high Force Feedback settings, is hardly noticeable.
This optimization is a crucial aspect of Fanatec's product development, aimed at not only matching but surpassing competitor products.