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Modified Rear Subframe and Trailing Arms
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Executed by Jake Larson

Jake Larson - Modified E30 trailing arm Background: E30 M3 owner Jake Larson shows us his modified rear subframe and trailing arms. The subframe has been modified to allow independent adjustment of rear camber and toe. Note that this is not possible with the popular K-Mac rear eccentric rear trailing arm bushings, where an adjustment in either camber or toe will also effect the other measurement. Click here for more information on the K-Mac rear trailing arm bushings and how they work.

Jake Larson - Modified E30 subframe - toe adjustment At right and below we see the modification for toe adjustment on the rear subframe.

The eccentric bolt is actually a BMW E39 5-Series part:

p/n 33 32 1 092 310 bolt
(M12 X 1.5 X 98mm)

p/n 33-32-1-093-456 washer

Kits like these can be had from several sources. Or you can fabricate your own.

Jake Larson - Modified E30 subframe - toe adjustment A study of these photos will reveal how there eccentric bolts work to adjust both camber and toe. The eccentric parts of the bolt and washer are held in position by the welded on tab. Then the hole in the trailing arm mounting point is slotted. Thus, when the eccentric bolt is rotated, it ends up sliding the mounting bolt (i.e. pivot point) forwards/backwards or up/down (toe or camber).

Jake Larson - Modified E30 subframe - camber adjustment Here we see the adjustment modification for camber. The principle is exactly the same as for toe, except that the slots are rotated 90.

In this instance the camber adjustment is on the "inside" of the rear subframe, and the toe adjustment is on the "outside" of the subframe. But there is no reason really that this situation could not be reversed.

The nice part of this principle of adjustment is that camber and toe are decoupled. However, the negative aspect is that in moving the pivot points around, one is changing the roll center height, and also the camber/toe curves. The effect is unlikely to be all that great, but it was enough to force the BMW Motorsport factory racecars to implement the camber and toe adjustments on the trailing arm, so that the pivot points stayed fixed.


Jake Larson - Modified E30 subframe - camber adjustment The last of the E30 M3 DTM racecars actually had an adjustment for roll center height, as well as for camber and toe. One can find a picture of this mechanism, as well as a description of roll center in a semi-trailing arm suspension on this page.

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