i just have tried a 20mm Spacer for one REAR Wheel for a Test.
Its a little bit too much
cause my michelin 225/40 R18 Pilot Super Sport
comes small out of the BRZ-Body
I want it as clean as possible without any little issue.
So tomorrow i take :
15mm Spacers for Wheels Rear ( 30mm REAR Axle extent )
and 10 mm Spacers for Wheels Front ( 20mm FRONT Axle extent )