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

[mike100]

Originally Posted by zrss

Lowering didn't work out quite as I hoped. The nose is a little less than 1/2" inch lower. I removed the factory rubber pads, installed the VBandP pads, and reinstalled the shims (my car has a green spring), which the instructions said would lower it about a full inch. If I get ambitious I may remove the shims to get more drop and see if that gets me close to the 1" drop I was looking for.

I like the look of USAZR1's car but wonder if that's not a little too low, at least for the washboards they call streets where I live.

Don't be too hasty, the car will settle once it all the wedges and whatever takes a set. Drive it for a week. Additionally, if you had to remove a control arm and retorqued it in the extended position, the frame bushings try really hard to stay at that angle for a few days until it twists and relaxes.

I recently traded springs with another guy who wanted to lower his car (I wanted the stock ride height) and both our cars rode higher for a few days.

[USAZR1]

Originally Posted by zrss

Lowering didn't work out quite as I hoped. The nose is a little less than 1/2" inch lower. I removed the factory rubber pads, installed the VBandP pads, and reinstalled the shims (my car has a green spring), which the instructions said would lower it about a full inch. If I get ambitious I may remove the shims to get more drop and see if that gets me close to the 1" drop I was looking for.

I like the look of USAZR1's car but wonder if that's not a little too low, at least for the washboards they call streets where I live.

Our car looks really low but because the front & rear tires are about 1" taller,the front air dam is still intact. It's only scraped once,so far,and that was on a pretty gnarly driveway. The VB&P front spring is a lot stiffer than the stock unit but is very easy to adjust. Might need to adjust ride height again after I get back from Houston,Monday.

[PhillipsLT5]

You get it too low, you will be hitting, headers, spoilers, curbs, speed bumps etc
I would assume alignment needed after this
http://www.vbandp.com/instructions/c...c.html?start=5

[zrss]

Originally Posted by PhillipsLT5

You get it too low, you will be hitting, headers, spoilers, curbs, speed bumps etc
I would assume alignment needed after this
http://www.vbandp.com/instructions/c...c.html?start=5

Right. That's why I only wanted to lower the car about 1". I guessed that going any lower would result in scraping and might alter front-end geometry in a bad way.

As for realignment, that's needed. Even with less than 1/2" drop, the steering feels sluggish or lazy which I presume is due to being out of alignment. I'm going to follow Mike100's suggestion of driving the car a bit and giving it time to settle before I decide if it's low enough. Once I get the height where I want it, an alignment will be next.

Thanks to everyone for their input

[USAZR1]

Originally Posted by PhillipsLT5

You get it too low, you will be hitting, headers, spoilers, curbs, speed bumps etc
I would assume alignment needed after this
http://www.vbandp.com/instructions/c...c.html?start=5

I've lowered a bunch of cars,including Corvettes,so it's nothing new to me.
Yes,the shop did a four-wheel alignment on our 94,when finished.

[WVZR-1]

Originally Posted by zrss

I'm going to follow Mike100's suggestion of driving the car a bit and giving it time to settle before I decide if it's low enough. Once I get the height where I want it, an alignment will be next.

Thanks to everyone for their input

Find yourself some 'rumble strips' on the side of the highway and towards the median, run both the left and right sides of the tires through about 50ft of 'rumble strips' and the suspension will be settled and you can go ahead with your alignment.

If you've replaced any suspension components or just some bushings and hardware the 'rumble strip' will prep it for the alignment, an alignment right after the replacement of components on the same rack without a drive is foolish.

[GOLDCYLON]

Originally Posted by PhillipsLT5

Call VBP, always helped me over phone

Yours is lowered Phil? Never noticed. Seriously....

[PhillipsLT5]

great Pic, yes mine was lowered and had some scraping issues, raised it up a bit, much better but it is still lowered some

[GOLDCYLON]

Originally Posted by PhillipsLT5

great Pic, yes mine was lowered and had some scraping issues, raised it up a bit, much better but it is still lowered some

Honestly never noticed Phil