strut brace - did I change anything?

[robrez]

Pardon my ignorance on suspension dynamics, but I just test fitted two strut braces to my m42 car. The first was an Eibach bar, which easily lined up with the studs on the strut tower. Then I installed a Racing Dynamics bar, and the holes on the brace where about half inch wider than the studs. So I installed one side first, then I jacked up the car on other side, got a little droop, and it popped right on. Then I lowered the car and tightened everything up.

With the RD brace still on, I put the Eibach brace over it and now the holes on the brace are about a half inch inward from the studs.

I know this sound like a dumb question but what accounts for the difference? Are my strut towers actually a half inch further apart now, and is my suspension geometry/alignment different now?

[jlevie]

It seems like there are two variants for the strut tower spacing on E30's. From IE's website:

"The BMW factory published body specification shows the distance between the strut towers should be 1002.2mm +-2mm (39.5"), measured from center to center (at the strut bearing opening in the inner fenders) - and the bar we manufacture is 1002.2mm, the published spec. However; we have found many cars (ranged across all E30 years and models) that measure about 980mm (38.75")... there is no published factory documentation of any difference in the body dimensions."

[robrez]

^^^ Thanks for the info., so basically, I put a wider strut brace on a car with narrower strut towers (I don't know whether the car came that way or the towers had slightly shifted over time).

Now does that essentially push the towers apart or correct the slight collapse? And if so, does that change the alignment? Thanks

[e46s54dr]

If you pushed your strut towers outwards by half and inch, it'll definitely change your alignment. Though it probably only changed it slightly so there's a chance you're still within spec. Does the car still track straight? Easiest way to check your alignment yourself is by setting both wheels parallel as if you are going down the road straight and measuring the length between the two front wheels. You can measure from one outside edge to the other outside edge or find any symetrical reference point. Measure both the length from front to front and the length from back to back of the wheel. Both front and back lengths should be relatively equal. My instructions may be a little confusing but it's a very easy process.