My car sits on coilovers, with Koni adjustables ('88 325iS with the GC track kit)
When we put the new wheels on we were questioning if my car was at the best ride height for handling. What I've always "heard" is that you want to the front control arms to be parallel with the ground when the car is at rest on the ground.
Is this true?
But that only takes care of the front? Do you then just set the rear ride height based on corner weighting needs?
As for setting the rear ride height relative to the front, here's a good way to start:
measure the stock rake, lower the front to where you like it (I've heard the level control arms thing too) and then set the rear ride height to match the stock rake...
you'll know it's too low when you crack an oil pan on a speedbump or road debris. i put two of tho$e on my '88 325is in the span of a month, back a few years ago.
You know it's too low when it can limbo better than you.
Does anyone know what the deal is with level control arms? I always thought it was because when you compress independent suspension, the geometry changes and your alignment goes crazy while it's compressed. If you start with your arms in a strange position and compress them, your geometry is affected more with every inch of movement.
How low is too low?
There is no such thing. ;)
I've regularly driven cars with an inch and a half of clearance, and a friend of mine regularly drove his min-truck with 3/8ths of an inch of clearance. ;)
My '63 Comet will scrape on ants turds. 
They say your control arms need to be level because otherwise the center of gravity and roll center get all out of whack. The way I've understood it is the closer the CoG and the roll center are together, the suspension will generate less roll. But when you lower it where the arms are not parallel anymore, the CoG gets lower and the roll center gets higher, and evidently that will make the suspension generate more roll. However, when you lower the car you generally have stiffer spring rates/dampers and bigger anti-roll bars. I suppose it depends on the suspension geometry of your car, but I think it applies to all MacPherson strut suspensions.
Also when the geometry gets out of whack like that, camber curves start to change. If I remember right, if the car's lowered too far it will start to generate positive camber under load instead of progressively gaining negative camber. Plus you have to start worrying about bump steer and losing travel of the suspension. I'm not sure that's all correct, so hopefully someone will step in and clarify a little more.
My TR3's front end is too low. It's about 4.25 inches off the ground at the lowest point, which is the U-bolt bracket for the sway bar. One U-Bolt is half worn away from grinding on speed bumps and higher angled driveways. It is defnitely too low, but won't be fixed until I finish restoring the TR6 suspension parts I will be installing. Maybe next winter. Until then, maybe I should get new U-bolts and replace them.
We do not ever hit the pan and very infrequently the chassis. It's just those sway bar mounts.
Jack
Jack wrote: My TR3's front end is too low. It's about 4.25 inches off the ground at the lowest point, which is the U-bolt bracket for the sway bar. One U-Bolt is half worn away from grinding on speed bumps and higher angled driveways.
Wow. I've always wondered how people manage to do that, when I didn't grind anything down daily driving in cars like my Falcon, pictured above, with only an inch and a half ground clearance at the front crossmember.
Even my relatively tall Fiat was 3" off the ground at the crossmember and it didn't hit anything.
From everything I've read thus far, it depends a lot on the car.
Lowering a Mk IV VW = bad news for suspension geometry. Apparently, raising the front end improves the roll-center... 
Lowering a '90's Civic = actually helps if not taken to the extreme...
Probably one of the numerous suspension theory books will do more good than anything you'll read on this forum. Grassroots and DIY does not mean anti-book learning. ;)
How low is too low?
Ian F wrote: From everything I've read thus far, it depends a lot on the car. Lowering a Mk IV VW = bad news for suspension geometry. Apparently, raising the front end improves the roll-center...
This is true, but there are lots of E30 guys one here, so I was hoping someone might already have the answer.
Chris_V wrote:Jack wrote: My TR3's front end is too low. It's about 4.25 inches off the ground at the lowest point, which is the U-bolt bracket for the sway bar. One U-Bolt is half worn away from grinding on speed bumps and higher angled driveways.Wow. I've always wondered how people manage to do that, when I didn't grind anything down daily driving in cars like my Falcon, pictured above, with only an inch and a half ground clearance at the front crossmember. Even my relatively tall Fiat was 3" off the ground at the crossmember and it didn't hit anything.
The front sway bar mounts are way up in front of the wheels and hang pretty low, so they can hit stuff before the tires start to raise the front end up.
Jack
Ive drove a few static dropped vehicles and never had a problem. Chris is right, no such thing as too low. Static drop, hydros, air bags, I like them all. The only stuff that is dumb lowered are 4x4 trucks and SUVs.
Lowest vehicle I ever drove regularly was my 88 GTI 16V. Tucking 15's and you couldnt fit a cigarette pack on its side between the frame rail and ground.
Didn't Steve Dinan write something about the ill-effects of lowering a cars suspension back in the 90's?
z31maniac wrote:Ian F wrote: Probably one of the numerous suspension theory books will do more good than anything you'll read on this forum. Grassroots and DIY does not mean anti-book learning. ;)This is true, but there are lots of E30 guys one here, so I was hoping someone might already have the answer.
Fred Phun's how to make your car handle is one your looking for here.
what you want is to ensure that the roll axis is close to parallel as you can get it, generally that is...
the roll axis is the imaginary line that connects the 2 imaginary roll centers front and rear.
inclination of this axis will affect your handling. (ask me, i have a mustang 
front center about ground level and rear at about the center of the axle)
Phun can tell you how to find the centers....
on the E30, watch the oilpan, consider a skidplate... replacing them in the car is possible, but a PITA.. (i shattered mine last summer)
Most strut suspensions suffer when lowered. The roll center gets lower, but by a disproportionate amount. To offset this people generally use really stiff springs. Also, when the control arm (actually, not the arm, but the imaginary line from pivot to ball joint), goes beyond parallel, your camber goes positive under compression
I dont know the particular answer for an E30.
stuart in mn wrote: How low is too low?
I'd ask if its even possible to drive that car but its too badass to be worried about silly little things like that. Back to the topic at hand, I'm not sure how much travel the E30s have but I know Miatas suffer from a lack of travel in the rear when lowered and that kills the handling. This can be alleviated but its still something to watch out for.
Lowering too much can put the roll center below ground level which is not a good thing.
iceracer wrote: Lowering too much can put the roll center below ground level which is not a good thing.
Yes, that is not good, but it's not the end of the world either. Every stock TR3 has a front roll center 3 feet below ground. The rear live axle has the roll center at axle height, so the two ends of the car are dancing to different drummers, but it can be made to handle quite well anyway.
Jack
stuart in mn wrote: How low is too low?
Hope there's a sun roof on that!
How Low is too low? When you can't get it back into the garage ! ( Mine has a 1" lip)
I usually point one exhaust clamp down to act as a "feeler"
It's Fred Puhn, by the way. In case anyone's looking for the book :)
Remember that your car doesn't operate at the static ride height. The suspension's always moving around. A well designed suspension will keep the roll centers under tight control regardless of where you start. However, any suspension will have odd behavior as it reaches the limits of its travel, and if you lower the car excessively then you'll be operating near these limits more often. Still, we have to consider the idealized example of a car at a constant cornering speed on a smooth road if we're going to discuss this, and that's where the static ride height is a basic dimension.
The Miata has excellent roll center control - I think that's why it handles so well and so consistently. A 323 GTX has atrocious geometry from what I've seen, and lowering that car will raise the roll center (at static ride height) causing increased roll.
Ryan9118 is thinking the right way, but generalizing a bit much. The behavior of the camber curves is going to depend on the geometry of a specific suspension, not simply whether it's strut or double-wishbone. But it's not actually the lower control arms that need to be level, it's the inner and outer pivot points. Look at a Miata control arm, and you'll discover that the control arm does not follow a line through these two points.
Lowering the car lowers the CG, which is good because it cuts down on weight transfer (our enemy) and the resultant roll. But when you lower a car, you not only affect your geometry and roll centers, you're also affecting your suspension travel. And this is something that's ignored by too many people. When you hit the bumpstops, your spring rate jumps dramatically and your handling goes screwy as the weight transfer changes dramatically and one end of your car basically turns solid. It's no coincidence that the lap record for Miatas on our local track is held not by the car with the most power, but the one with the most wheel travel. This loss of wheel travel is one big reason you need to run stiffer springs when you lower a car.
The other reason is the old adage, "any suspension will work if you don't let it" :) If you restrict the movement by simply making it too hard for the suspension to move, geometry no longer matters.
Cornerweighting won't affect your rear ride height, really. You can't shift weight front/back with cornerweighting, only diagonally. A good mechanic will manage to keep the ride height and stance exactly the same when putting it on the scales.
So for static show cars and rat rods, there's no such thing as too low. That's because the look is the most important thing. But if you're worried about handling, there's definitely a "too low".
Keith wrote: The other reason is the old adage, "any suspension will work if you don't let it" :) If you restrict the movement by simply making it too hard for the suspension to move, geometry no longer matters.
The go-kart theory of suspension design
Keith wrote: A 323 GTX has atrocious geometry from what I've seen, and lowering that car will raise the roll center (at static ride height) causing increased roll.
This is the case with any McPherson strut design. Lowering moves the angle of the lower arm while the top remains fixed.
GameboyRMH wrote:Keith wrote: The other reason is the old adage, "any suspension will work if you don't let it" :) If you restrict the movement by simply making it too hard for the suspension to move, geometry no longer matters.The go-kart theory of suspension design
Kinda... except the Go Karts rely on lifting a tire in the corners, due to chassis flex. They run ridiculous amounts of caster (20 degrees or so), very little camber, and a lot of the tuning is done by varying the wall thickness/diameter of the rear axle.
never toooo low
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