There are two major problems with the OEM rear lower control arm on the BRZ/FR-S/GT86:
1. It doesn’t offer any camber adjustment
2. It is very weak under longitudinal loading
Originally, I was going to try a shim stack design for the rear lower control arm. However, I was unsatisfied with the design because it would either be too heavy or too soft. So, I went back to the drawing board and started from scratch. This time I went with a threaded rod adjustment rather than shim stacks because the shims were adding too much mass. This is the design:
With a threaded rod design, we were able to reduce the mass of the arm while increasing stiffness. Here you can see the stress plot side-by-side. The OEM arm:
Note how twisted the arm becomes where the arm tapers. Under extreme loading, the arm is likely to break at the welds. Our arm:
Our FEA results show that stress is reduced in the arm by 900%, and stiffness is increased by 1100% while maintaining the same mass.