The E82 1-Series M and E90/E92/E93 M3 received different control arms than their non-M counterparts. With the exception of shock absorbers, strut assemblies, and springs, these control arms vary in several ways and are a critical part of what makes the 1M and M3 handle differently. Below is a comparison of the front and rear control arm suspensions and how they vary.
The front control arms set up are identical in that it features two tension struts and two lower wishbones. However, that's where the similarities end. The control arm design itself is what makes the difference. The tension struts (big curved control arms) feature a solid rubber inner bushing that reduces deflection and eliminates the hydro bushing weakness, tearing, and leaks. The solid rubber bushing is stiffer, which helps tighten up the front suspension without being overly stiff and unforgiving. The lower wishbones (straight control arm) feature a sealed inner bearing, also known as a monoball, that allows the inner part of the control arm to rotate more freely compared to the non-M rubber bushing. This design change also allows for added durability in the long run. The lower control arm is slightly longer, adding approximately .75° of negative camber, helping reduce understeer and drastically improving turn in response without significantly impacting tire read life.
The rear control arm suspension drastically differs on the E9X M3 and E82 1 Series M compared to their non-M counterparts. The non-M upper control arms are rolled steel and feature traditional rubber bushings in both the inner and outer positions. The "hollow" design of the OE control arms is weak and flexes a lot, particularly under acceleration. The M3 version of these upper control arms is made of solid aluminum and is light compared to the non-M variants. Similar to the front wishbone, the upper wishbones use a monoball mount, allowing free movement of the control arms under all conditions. This helps keep the suspension stable and planted under all conditions.
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