Help Lowering My Z

[batchman]

There's something that anyone lowering their car should look at before calling it done. Not likely to be a problem on a C4 unless you're going to the modern "big wheel" look and slamming the height, but I figured it worth adding to the discussion.

From front, look at the control arms - they should still angle noticably down toward the wheel.

Similarly from the back, the halfshaft should still angle down toward the wheel.

Now for my bastardized description of why:
This is important to keep suspension travel from changing the virtual length of the arms too much. If you go so low as to start at rest with either of these angling up, you will have pronounced changes in the virtual arm length through jounce - making some surprising dynamic alignment changes.

To demonstrate this, take a ruler and grasp it at both ends, holding it horizontally. Move one end up/down 1" and notice the small change in the "x axis" distance between the two ends. Now repeat the experiment with the arm starting at a 15degree angle - much greater change in the "x axis" length for the same up/down motion. Now picture how this gets more complicated when you add a second arm of a different length.

Since the tire load is on the outside of the corner, it's more predictable if you prioritize this motion in jounce than in rebound, in other words that's why you don't shoot for dead level at rest.

So if you find you get odd handling after lowering the car (right when you don't want it!) this is something to look at.

I should add the C4 wants some "rake" to it - keep the rear higher than the front - since the rear suspension gets more stray motion (toe change) through its' sweep. This is why performance alignments run what seems like a lot of rear toe-in, it's pre-compensation so that it's about right when heavily loaded.

HTH,
- Jeff