First off I'd like to say that this wouldn't have been possible without the work that was done by Orb, Mr5 and Harold from HP Autowerks over on e90post. These guys did the preliminary R&D work for retrofitting some of these components on the E9x platform and inspired me to do the same on the E89.
To reduce costs BMW leveraged several exiting parts from their bin when building the suspension for the E89. Up front the tension struts and swaybar endlinks are the exact same as used in the non-M E9x platform. In the rear, the lower wishbones (camber arms) are lifted from the E85 platform while trailing arm brackets are the same as the E46. This opens up the possibility of improving the suspension performance on the E89 by using the same "parts bin" approach".
Note, I assume no responsibility for damage to your car if you perform the upgrades outlined. Always have suspension components installed by a professional who can also do an alignment at the same shop. DO NOT drive your car without an alignment after performing this upgrade.
Since I haven't seen any of this information posted here before I decided to do the research and be the guinea pig. I wanted to maintain the OEM electronic dampers but improve the overall handling experiance. Initial results are....
Front Suspension:
I've used the tension struts from the E92 M3 along with stock M-Adaptive struts and Eibach lowering springs (1.2" drop). The M3 wishbones are the correct length (maybe a tiny bit longer), but unfortunately have the headlight leveling sensor attachment on the wrong side of the car. The main difference in the M3 tension struts is the rubber bushings which are much stiffer than the stock hydraulic isolators. To correct the geometry of the front sway bar with the lower ride height I plan on installing adjustable swaybar endlinks for the E90 from HP Autowerks, but will let the car settle a bit before installing.
Here are the part numbers for the M3 bits:
Left tension strut with rubber mounting 31102283575
Right tension strut with rubber mounting 31102283576
Since several bolts/locking nuts need to also be replaced I would suggest ordering all the M3 components as a complete kit from HP Autowerks along with the endlinks.
Installation is fairly straight forward. Here are the torque specifications:
Tension strut to steering knuckle
(replace with new) 165 Nm (122 ft-lb)
Tension strut to subframe
M12 8.8 (replace with new) 68 Nm (50 ft-lb) + 90 degree
M12 10.9 (replace with new) 100 Nm (74 ft-lb) +90 degree
Rear Suspension:
In the rear I replaced the stock lower wishbones with adjustable E46 camber arms from Turner Motorsport and Eibach springs (0.8" drop) on the stock M-Adaptive shocks. On the camber arms I opted for rod-ends over rubber bushings to reduce deflection with a small sacrifice in ride quality. Although the E85 and E46 don't share the exact same part number for the camber arms, the Turner arms work fine as the length can be adjusted. In addition, other compatible parts include Turner trailing arm bushing limiters which use the stock bushing but incorparate aluminum shims on both sides of the bushing to limit travel.
Unfortunately the actual bushing where the trailing arm mounts to the chassis is unique to the E89 otherwise an upgrade to the E46 M3 bushing may also be an option. I may still grab a set of the E46 M3 bushings to do a proper comparison as both the balljoint and hub bushing share part numbers with the E46.
Installation of the camber arms is a fairly invovled job as the rear diff needs to be partially lowered in order to remove the inner bolts.
Here are links to the parts on Turner's website:
http://www.turnermotorsport.com/p-96...-shim-kit.aspx
http://www.turnermotorsport.com/p-35...reettrack.aspx
Alignment:
It is absolutely crutial to get a full alignment after completing this upgrade. Here are the OEM alignment tolerances for the E89:
Front Camber -0.1 to -1.1
Front Caster 6.5 (fixed)
Front Toe 0.02 to 0.22
Front SAI 14.2 (fixed)
Front Inc. Angle 13.6 (fixed)
Rear Camber -1.9 to -2.8
Rear Toe 0.05 to 0.25
For my car I was looking for the following targets post suspension upgrade:
Front Camber -0.5
Front Toe 0.06
Rear Camber -2.5
Rear Toe 0
Actual alignment results were very close to the targets.
To get a bit of additional camber in the front, the alignment pin can be removed from the top of the strut mount. This allows you to slide the top of the strut in towards the engine a bit more. As a future upgrade I will likely install camber plates and have confirmed that Ground Control has them available for the E89 (should be the exact same mounting as the E9X anyway).
I will be taking the car on the track in the next week to see how the handling feels at the limit. I plan to add in the H&R adjustable rear swaybar soon, but wanted to get a chance to test just some of the upgraded components first.
I've attached a few pics of the install...