Hi,

I've searched for a few things and I'd like to consolidate some points that I've read WRT suspension height and stiffness.

I've read a few things that say that a 1st gen needs to have the rear of the car, overall, lower than the front to "align the roll centres". The difference I've seen spoken/written about is about 10mm (or .4 of an inch, near enough to 1/2 an inch).

What ride height do the typical aftermarket springs in the US have a 1st gen at? What, if anything, is the "ideal" suspension height front and rear (and yes, I am looking for peejay to bite here).

Ben

 

NO NO NO. You do NOT want the rear roll center aligned with the center of gravity, which is what happens when you lower a lot and retain the Watts link.

 

Ri-ight. Because that increases binding of the Watts link, yes?

So, let's assume that I want to keep the standard suspension geometry but can afford new shocks, springs sway-bars and bushes. What do I do?

 

No, it's because when the CG and the roll center are in line, the suspension doesn't move at all. It just picks the inside tire off the ground. Nothing to do with what kind of linkage it has, it's simply the sideways forces (the CG) pushing directly on the suspension's virtual pivot point (the roll center).

 

OK, then.

Let's talk numbers. Ride height front and rear? Spring weights/rates? Sway bar presence or absence? Front and rear sway bar thickness?

 

Buy the g-force engineering 1st gen setup manual... So I can read it!

http://www.gforceengineering.net/products.htm

 

No one said anything about aligning the roll center with the center of gravity. I believe the articles he's refering to were talking about aligning the FRONT and REAR roll centers. What's your take on that?

 

Exactly.

This is the start of the article:
http://www.whiteline.com.au/articles/RH99_RX7_a.htm

Ben

 

Making the roll COUPLES the same front/rear is more important. The rear roll center is fixed, in this case by the center point of the Watts linkage which is a fixed point on the rear axle so it pretty much stays in the same place with respect to the ground. The front roll center is a geometric point defined by first measuring the point where the line defined by the lower ball joint and inner control arm bushing meet a line that is 90 degrees to the top of the strut shaft, then making another imaginary line front that geometric point to the tire's contact patch. Where that second (third, really) imaginary line meets thecorresponding line from the other side is where the front roll center is. (NOTE that the front center can and does move around when the car is leaning - this can be good, or bad, depending on how it moves)

The roll *couple* is the distance from the CG to the roll center - how much leverage the body has on the suspension.

To make the roll couples the same front/rear, you need to lengthen the rear roll couple and shorten the front. In the rear you either lower the rear roll center (Watts link) or you raise the CG away from the roll center (lifting). In the front you either raise the front roll center by ball joint spacers (go between steering arm and strut body, to change the angle of the lower control arm's line) or... by LIFTING.

Now, grasshopper, you SEE the method to my madness. MADNESS! AH-hahahaha!!

- Pete (cue dramatic thunderclap)

 

Can you see how my rear end is jacked up?
I'm running 260s on the rear, it's nearly two inches higher than the front, which sport 205s, Konis adjusted pretty stiff, RB springs, and the rear bar is still in place (with the help of matching 1/2 inch driver sockets used as spacers.
One would think it would be squirrly as hell, but I can drift perfectly balanced if I try, though it does have more push.

Did I just get lucky? I mean, it's such a cob-jobbed set up all in an effort to shoehorn those nasty tires I happened to have into the fenders.

 

I dunno, if you didn't change the distance between the rear axle and the body, you didn't alter anything meaningful as far as geometry goes.

Well cancel that... you'd have raised the CG and roll center at the same time, for the same distance, so the rear's resistance to leaning is the same but now the car wants to lean more since the CG is higher off the ground - resulting in easier to unweight the inside rear tire.

 

Ah, but if the 260mm widen the stance, then the moment to lifting that inside tire is longer and reduced.