Quote:
Originally Posted by wmandra
nicknaz/janissa,
I'll try and address both of your questions the best I can. First, in regards to this setup vs an aftermarket setup for an E89, there is no complete aftermarket suspension setup for the E89 platform currently available. If you are talking about a coilover setup, which I'll address below, that still leaves a lot of other suspension components stock.
A suspension is very complex with a number of components that each individually play a part in how the car handles and feels. Springs and shocks control the vertical movement of the wheel when cornering or driving over any kind of bump. Other components, like the control arms and bushings, are also important. If the bushings used are too soft (which the stock hydraulic isolators are) they can deflect under load. This deflection can change the geometry of the suspension, even if just slightly. In a full blown race car many of the bushings are eliminated and solid joints used instead but the ride would be so harsh on the street that you'd never want to drive it. So everything is a compromise, trying to find the right balance of stiffness and comfort.
Here's a quick summary of the various components, stock weaknesses and possible solutions. Every single one of these items will have some impact on the overall suspension and handling:
Front tension struts:
Stock - soft bushings which will deflect under load
Upgrade - replace with ones from E9x M3 which have stiffer rubber bushings.
Effect - less deflection in front toe with a little more vibration transferred into the steering wheel. Will help reduce under steer.
Front wishbones:
Stock - soft bushings that will deflect
Upgrade - none currently as the headlight leveling rod is on the opposite side on the E89 and E9x. Still working on some possible solutions here
Front upper spring perch / guide plate:
Stock - no real "issue" other than stack height and lack of adjustment.
Upgrade - replace with ground control or Vorshlag camber plates.
Effect - camber and caster adjustment. lower stack height on the camber plate will give more travel in the strut when lowered
Front springs / struts:
Stock - no ride height adjustment. minimal adjustment to rebound possible (comfort vs sport mode)
Upgrade - fully adjustable coilovers or lowering springs
Effect - lower/adjustable ride height (also allows for corner weighting). adjustable compression and rebound can be made stiffer at the sacrifice of ride quality.
Front sway bar end links:
Stock - no real "issue" at stock ride height. Incorrect length when car is lowered causes geometry to be off.
Upgrade - adjustable sway bar end links
Effect - sway bar geometry restored so that frame mount and end of bar on same horizontal plane increasing effectiveness
Front sway bar:
Stock - a little on the soft side which can lead to under steer and limited roll control
Upgrade - replace with H&R 27mm sway bar
Effect - reduction in under steer, better roll control and turn in response
Rear lower wishbone:
Stock - no adjustment for camber, soft rubber inner bushing which can deflect under load
Upgrade - E46 adjustable rear camber arms with inner bushing replaced with rod end (solid mount)
Effect - large adjustment range for rear camber. slightly rougher ride with rod-end, but no deflection under load.
Rear trailing arm bushing:
Stock - lots of deflection under load will cause rear toe to change during hard corners
Upgrade - E46 rear trailing arm bushing limiters. These are just shims that are installed on both sides of the bushing greatly reducing deflection
Effect - rear toe maintained under hard cornering, no impact on ride quality
Rear trailing arm upper ball joint:
Stock - no issues, part used in E89 is the same as E46 M3 which is already fairly stiff
Upgrade - none
Rear trailing arm lower ball joint:
Stock - rubber bushing that will deflect under load
Upgrade - none. unfortunately BMW used a different size lower bushing in the E89, in the E85 and E46 this could be replaced with the better upper ball joint.
Rear upper wishbone inner ball joint:
Stock - rubber bushing that will deflect under load
Upgrade - Turner E46 monoball or Group N E46 bushing
Effect - Group N bushing uses stiffer rubber than stock will reduce deflection; Turner monoball replaces rubber bushing with a bearing that will not deflect.
Rear springs / shocks:
Stock - no ride height adjustment. minimal adjustment to rebound possible (comfort vs sport mode)
Upgrade - fully adjustable coilovers or lowering springs
Effect - lower/adjustable ride height (also allows for corner weighting). adjustable compression and rebound can be made stiffer at the sacrifice of ride quality.
Rear sway bar:
Stock - a little on the soft side which can lead to under steer and limited roll control
Upgrade - replace with H&R 21mm adjustable sway bar
Effect - increase in over steer, better roll control
Rear sub frame bushings:
Stock - rubber bushings that will deflect
Upgrade - none currently. still investigating
All of the above can be broken down into various "stages" (these are just mine, but feel free to define your own):
Stage 1:
- Stock struts/shocks (with adaptive suspension)
- Eibach or H&R lowering springs
- Front M3 tension struts
- Front adjustable sway bar end links
- Rear adjustable camber arms
Stage 2:
- Everything in Stage 1
- H&R front and rear sway bars
- rear trailing arm bushing limiter
- rear upper wishbone inner ball joint replacement (Group N or Turner)
Stage 3:
- Everything in Stage 1 & 2
- Vorshlag or Ground Control front camber plates
- Fully adjustable coilovers
- rear subframe bushings (if available)
Hope this helps....
Bill
|
Thanks for this post. I was just searching around for some suspension mods for after i get my turbos upgraded. This helps alot.