Rubber bushings found in the M4’s rear upper arms are the last weak link in an otherwise rigid suspension. The original BMW bushings yield to cornering forces applied to the suspension, resulting in camber and toe change that is not ideal for performance driving. Fall Line’s kit replaces the soft upper control arm bushings with military spec Aurora brand spherical bearings, enabling the rear suspension arms to move smoothly through their travel and giving the rear of a car a more solid, planted feel. The reduced geometry change allows for the car to retain its desired alignment, maintaining better control over the tire’s behavior under heavy load.
The F8x M cars feature a subframe that is directly mounted to the chassis by BMW M, to reduce suspension compliance and improve performance and driving feel.
Similarly, the Fall Line upper control arm bearings rigidly mount the suspension arms to the subframe, increasing driver feedback, reducing geometry change, and improving performance. As with any elimination of suspension bushings, more feedback does equate to more road and suspension noise. While the Fall Line rear upper control arm bearings are a substantial performance improvement, please do be prepared for increased noise, vibration, and harshness after installing the parts.
Price is per set of 4, as there are 2 per side.