Hello @Everynone and thank you for your reply.
The game runs on physics. Move-forward is made by physics constrain on a wheel and setting the rotation and strength of the Physic Constrain… setting physics materials… friction, gravity…
So to add “world/relative rotation” all the time is math beyond my skill. I am for example scared that adding world/relative rotation would not react with angular damping…
Or I think I would have to create a function with a big math in it…
If I add torque force with a button press, math is taken care of by the engine 
So when I decide how to rotate, I do not want to put direct value into world rotation, but I prefer to affect the physics.
Anyway, I will read a few more times what you wrote to get it and then I think I will try to playtest the Lerp option by adding torque force to the rotation vector.