Originally Posted by rbakker

It has nothing t do with what you are saying, it has to do with simple mechanics.
The way the cars are designed, the forces introduced in the chassis by the braking system (servo to brake cam) and the pulling force of the side belt. Both give a torque moment in the chassis that makes it bend, next to that the rear wears due to contact with the tarmac.

Just put your blocks when adjusting the downstops under both axles fr+rr during setup and you will be ok,
when you start driving al your laps within 0.2s. then its time to change the chassis once in a while.