This is a variation on Powerflex’s basic kit. iWe also got upper rear strut mounts and adjustable rear control arm bushings.
The front control arm bushings are offset, like an E30 M3 for more caster. This helps with high speed stability.
The optional rear control arm bushings have adjustability for camber and toe, helping to offset the negative effects of a lowering spring kit.
The rear upper shock mounts were replaced with these Powerflex units.
Powerflex also makes a low price rear differential mount. E30 BMWs are notorious for tearing up old, stock rubber differential mounts when driven hard.
For our last installment on the suspension, it was time to replace the BMW’s bushings. Our 318is came with rubber suspension bushings that—while still mostly usable—were now 25 years old. We could have replaced these bushings with new stock pieces, but we opted for Powerflex chassis bushings for two reasons: the unique polyurethane material offers less chassis flex without the harshness and noise of some other urethane options, and these bushings offer increased ability to alter suspension settings. This means adjustability for camber and toe in the rear and more toe in the front, building in much better handling and keeping the wheel alignment correct when used with lowering springs.
If we had used only lowering springs without the added adjustability of the new bushings, we would have added so much negative camber at the rear of the car that we would have faced dramatically increased tire wear. Every chassis tuning decision is a compromise between handling and ride comfort. Again, we want this car to be a competent daily driver in addition to occasional track use, so we just could not abide by that. However, we are willing to put up with the slightly stiffer ride these bushings theoretically produce.
On the upside, Powerflex has four different stiffness levels available so they can engineer the bushing the correct material for the specific application, meaning it's stiff when you need it and compliant when the fitment requires it. General harshness for the sake of being stiffer is minimized. Thankfully then, the materials used in these bushings are soft enough that the degradation in ride quality is barely noticed, while the improvement in; turn in, steady state cornering and under braking is noticed instantly.
The other good news is once you have the subframes out on the bench, installing Powerflex bushings is a straightforward process that will take less than a couple of hours.
A full set of Powerflex bushings installed on your E30 chassis will set you back less than $400 and includes a new differential mounting bushing and rear subframe mount bushings, which when combined, reduce the amount the differential and rear subframe movement while the rear of the chassis is pushed. We did opt for the optional adjustable rear control arm bushings that allow for camber and toe adjustment. They start at $230 (again to correct and adjust alignment when using lowering springs).
Up front, we used offset front control arm bushings. The move to offset bushings (used in E30 M3s from the factory) offers more toe to increase stability at high speeds, which our overhauled engine is more than capable of sustaining.
The final product we used from Powerflex is their upper rear shock mounts. E30, E36 and E46 BMWs tend to tear stock upper rear strut mounts out when stiffer than stock dampers are used, so these Powerflex mounts are highly recommended. Not only do they offer more precise control, but they also reinforce the chassis in the attachment area.
Anti-roll bar bushings are also available, but we skipped these, as the Eibach anti-roll bars we installed came with similar bushings.
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