Subframe Spacers 0mm, 10mm, 20mm

[E30SPDFRK]

I don't normally argue about stuff on here but this is incorrect and misleading for someone looking for solid info in the V8 subforum. Lowering the subframe would absolutely affect bump steer in a negative manner.

How do you figure? They will still have the same curves, they're just further along on them.

The steering rack mount and lower control arm pivot (ball joint) are both on the front subframe. Moving the subframe does not change their relationship to each other.

Anti dive would be slightly affected because the rear control arm pivot stays fixed, but any meaningful amount of bumpsteer has not been introduced.

This is what I'm saying. And by rotating the offset CAB's you should be able to get the anti-dive pretty much back to normal.

[The Dark Side of Will]

/\ This. The spacers won't change the shape of the bump steer curve... they'll just move the suspension to a different point on that curve.

I think it's reasonable to expect that BMW would set the suspension up so that their static ride height was the minimum point on the bump steer curve. This means that changing ride height puts the suspension at a point on the bump steer curve that probably has more bump steer than stock.

However, the shape of the curve is still the same as stock.

I wasn't talking about getting anti-dive back to "normal"... I was talking about playing with it.

[dirty30]

How do you figure? They will still have the same curves, they're just further along on them.

Because they don't have the same curves, thats how I figure. The tie rod/ control arm relationship is only designed to work when the curves are near parallel to each other, at the extreme end of that suspension cycle the curves are very far away from each other, resulting in bump steer. Lowering the subframe pushes the control arms and tie rods further up in their cycle, away from the "parallel" area creating bump steer.

[The Dark Side of Will]

By "bumpsteer curve" we do not mean the relative paths of the tie rod end and outer ball joint. We mean a plot of relative toe change vs. suspension travel, referenced to static ride height.

The ideal situation is that this curve is a straight line with zero slope. Almost nothing actually does that.
As long as the suspension pivots are not moved relative to each other, the shape of that curve stays the same. So lowering the car and adding subframe spacers both have the same effect in that they change the reference point on the curve that represents static ride height, but do not change the shape of the curve. If this point moves to a place on the curve that has a steeper slope than the stock ride height, bump steer will get worse.

Will that be a problem? I have no idea, as I've never seen a plot based on actual measurements of E30 bump steer.

[slammin.e28]

Hypothetically, running 20mm spacers, would it be a good/bad/terrible idea to run e90 drophats?

Figure we're talking about running with stock suspension so as to keep it simple.