[piper6909]

Originally Posted by The Radium King

so, the oem trailing arms are on a ball at the inner connection point - as a result the outer end of the arm can move up and down as well as in and out.

the eps trailing arms are on a bushing such that they can move in and out but not up and down.

the inner trailing arm connection point is tied to the body of the car and is fixed, however the outer point is tied to the control arm. the control arm moves up and down as the damper compresses and rebounds and, as a result, the outer end of the trailing arm needs to be able to move up and down. note that the role of the trailing arm is not to resist the up/down motion of the control arm, but rather to keep it from moving forward/backward (caster).

the eps trailing arm bushing doesn't allow this motion, but the suspension still has to compress; as a result the deflection occurs in the arm itself.

making it all worse is the design of the arm itself. if you look at it, it looks like a little 'I' beam. I beams are designed to be strong in one direction; how the eps arms get loaded is the perpendicular direction - where they have no strength (on the front, anyways).

Thank you for explaining it better than I did!