<E24><E28> Suspension, Re: M6 suspension upgrade

[Pete Read <pete.read@xxxxxxxxxx>]

Dennis Logan asks:
>I currently own a 1988 M6 that I want to upgrade the suspension and 
>to lower the car about an inch.
>I previously owned a 635csi that I upgraded the suspension with a 
>Bilstein performance package that included progressive springs and 
>shocks that significantly improved that handling and lowered the car 
>about an inch.
>I want to do a similar upgrade to my M6. I know I have to buy the 
>parts to eliminate the self-leveling system as well as the performance 
>springs and shocks. It also is important to my to lower the car at 
>least an inch for a low profile look, but I do not want to lower the 
>suspension to much that the wheels are not parallel to the road,
>like / \. What additional part(s) are needed to insure that the wheels 
>remain parallel to the road.


Suspension Lowering increases negative camber
- ---------------------------------------------
Most independent suspensions camber in (get more negative, i.e. / \)
as they are compressed.  This is to compensate for body roll and
also prevents tire scrub as the suspension moves through its arc.
Your E24 suspension is typical because it gains negative camber
both front and rear as the suspension is compressed (the rear wheels
also toe-in because of the semi-trailing arm geometry).

Lowering springs create the same effect as compressing the suspension
because -- well, they make the car lower.  If the suspension is lowered
one inch, it's the same as compressing the suspension one inch.
You've lost one inch, out of about four total, bump travel and the
wheel has cambered in.

Wheel camber on the E24 and E28 BMWs is not adjustable in stock
form.  Offset strut bearings can be purchased to change the 
front camber a fixed 0.5 degrees in either direction.  The rear
trailing arms can be removed and slotted to make them adjustable,
but it's a big job.

To prevent excessive static negative camber, I'd recommend staying 
as close to the stock ride height as your aesthetic taste allows.


Mformation M5/M6 email list -- E24, E28 suspension articles
- -----------------------------------------------------------
You may be aware of this because you're on John Allen's M5/M6 
Mformation email list, but the Mformation archives contain 
quite a bit of suspension information.  The archives are all
big text files which can be downloaded and text searched with
any basic editor or word processor.  

I've posted several which may interest you (see below) -- these 
have also been posted to the bmw-digest, but I don't have the digest 
number.  Of course, I'm not the only one providing information, 
so a search on words like "suspension", "springs", "shocks", 
"bilstein", and "koni" will turn-up quite a bit of information.
If you're a real glutton for punishment, search on "Pete Read".

Mformation
Digest#      Subject:
- ----------   -------- 
  #22        M5 Suspension -- Part 1, Overview
  #88        E28 M5 Suspension Installation Procedure
 #172        Re: <E28><E24> Spring Rate Numbers
 #174        Re: <E28><E24> Shock Damping Numbers (Bilstein)

John Allen's M5/M6 Mformation email list information. Just point to:
   http://www.halcyon.com/jrallen/Mformation/

The archives of all the old Mformation digests are at:
   http://www.halcyon.com/jrallen/Mformation/archive/


All E24 and E28 Suspensions are the same, parts to check
- --------------------------------------------------------
Let me also point out that most of the suspension discussion on 
the Mformation list applies to any E24 or E28, not just M5s and
M6s.  

All E28s and '83-on E24s have the same basic suspension.  
Only the spring rates, shocks, sway bar sizes, and front 
sway bar frame mounts change.  Earlier, before '83, six series 
share suspensions with the older E12 five series.

The exception to E28s being all the same is the '82 528e.  It
has the old-style (E12) rear suspension, with the 20 degree angle
semi-trailing arms versus the newer Trac-Link 13 degree arms.
Basically five and six series are identical cars with different 
bodywork and interior trim.

When upgrading or working on your suspension, check and consider 
replacing the following wear parts:  

Front
- -----
Shocks, also called strut inserts
Strut bearings
Bump stops, absorbers (not needed for Bilstein front) 
Control arms and bushings
Steering linkage
Sway bar links
Sway bar rubber bushings

Rear
- ----
Shocks
Top shock mounts, guide supports
Paper gasket at top shock mounts
Bump stops, absorbers
Sway bar links, dogbones
Sway bar rubber bushings


  Pete Read
  '88 M5 
  Arlington, VA

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