I go through spreadsheet trying to make a Macpherson strut on both front and rear the chassis look fine , but not ingame the ingame result showing bumpy and strong tendency of rear tire driving forward and toe-in as accelerate any insight of the problems?
This really isn't related to chassis flex. I think you're imagining some/all of the arms are more fixed than they actually are. rF2 by default is expecting a-arms (wishbones), and they are then anchored as you would expect at the inside end. When you move away from that basic construct, you need to make sure it will physically work - ptool is good to check that your setup will work properly. You may need to add ori joints or ball joints to help constrain movement.
