99% of the time the rear brake balance will be 10
So begin with 10/10
The car almost always wil show understeer under braking entering a turn.
To take this understeer out till you feel good with it, just reduce the front number.
I didn´t check the BMW Z4 GT3 but i think it will be around 8/10
For the APP i´ll correct all the brakes balance.
To replace the tunes sheets for each car in mt GTP garage, this take more time because i hve to edit post by post.
But, i´ve writen a method at the post #1 about this.
All my brakes balance are wrong after 1.04. I´ll need some time to reset all this.
If you want to do yourself during this time, it´s easy.
-Set the brake balance at 10/10 all the cars.
-Then go on track and reduce the front number till you feel the car ok, showing a good eagerness entering a turn under strong braking and still steady on the driving line.
Enjoy your drive.