View Full Version : Suspension Geometry...

03-21-2003, 08:50 AM
Ok.. So I got All this fancy suspension stuff.. bars, and pillowballs, and adjustable arms OH MY!..

I've got is setup pretty well, this is what I got:
JIC Adjustable RUCA
Pillowball Tension Rods
Moog Tie rod ends
Cusco Tension Rod
Do-luck Front ladder bar
Greg dupree subframe sapcers
OEM Sway bars
Cusco OS Front STB (CF)
Cusco Rear OS STB w/ Triangle Bar

I'm not sure how far the car has been lowered from stock.. I didn't take before and after measurements.

Alignment specs are:
-2 camber
0 toe
+8 caster

-1 camber
.13 toe (this is more than likely from lowering the car with the OEM toe control rods
0 caster

My problem (which I have yet to fully diagnose) Seems to be that I am hitting the Rear bump stops on really tight slow corners. Like an Auto-x. Not hard, but it's there. Height of the car was adjusted with nothing but the strut mounting points, spring perch hieght has not been touched. At full droop the springs can be rotated on the perch with a little force.

It appears I have about 2" (maybe a touch more) suspension travel in the back, and probably 3-4 in the front.

I'm also having to run the front struts a good bit harder than the fronts.. out of 16 clicks front and rear.. they are at 11 front, 2 rear.

Any ideas on how to make the setup a little more balanced?

03-21-2003, 09:46 AM
How low is it?

Measure from the ground to the middle of the fender (top of arch) on all four corners. After that, I (or maybe someone with stock suspension) can measure for reference.

You might just have the thing too low to be effective.


03-21-2003, 10:01 AM
damn i typed a big reply and the computer took a crap. grr

ok um..
i have exactly the same setup (minus the moog) and i have never hit the bumpstops like you are. my car is lowered same too

my only thoughts
when you lower the car w/ the shock perch. you have to hold the spring perch to make sure it rotates at same the shock does. if not, the spring perch will be actally moving up when the shock is moving down. i did that once and the car's response was completely different.

that's all i can think of.

03-21-2003, 10:37 AM
eric - I'll get that this afternoon..

dousan - I made sure not to do that.. If I had done that, then the spring would be preloaded, and I wouldn't be able to rotate the spring on the perch. I actually unbolt the bottom of the strut from the upright, and then adjust height, tighten it back down, then bolt it back to the upright.

03-21-2003, 04:51 PM
Here are some height measurements I took from a stock '93 base hatch

LF: 15.5" (39.37cm) from the center of the axle to the top of the wheel-well cutout 9" off the ground (flat spot just next to the side skirt )
RF: 16" (40.64cm) 8.5" off the ground
LR: 15" (38.1cm) 8.5" off the ground
RR: 15.25" (38.735cm) 8.5" off the ground

Measuring from the ground to the top of the wheel-well cutout doesn't take into account the profile of his tires.

..But in this case, with the issue being stroke, with the JIC, the height shouldn't really matter..

Is there a significant amount of 'strut' coming up through the rear camber plates?

How much can the rear wheel drop when you lift the rear of the car off the ground? And how far will the rear wheel move when the wheel is first placed on the ground, and then settles to ride height? Spring rates?

Is it possible that the rear inside tire is picking up off the ground in the turn?

03-22-2003, 10:15 AM
my aligment is
-1 camber, .05 toe
-2 camber, .07 toe

Is it dificult to adjust the alignment? I wish I had -2 up front and -1 in the rear.

03-22-2003, 11:39 AM
how much travel is available from the JIC's? You said that you have 3-4" of travel in the front, does this mean that when you set the car down, there is 3-4" left in the travel? This would tell me that you have about 6" of total travel available. Is this the same for both front and rear? Do you know the exact amount of total travel available? If you have the same amount of travel available front and rear, then you should adjust the suspension so you have the same amount of sag on all four shocks. Sag is easily adjusted with preload, and that's why you have adjustable preload. Of course you can also adjust sag with spring rate, since a stiffer spring of the same extended length will sag less with the same amount of static load. If you are getting a lot more sag on the rear then the front, and you would like to reduce that, I would use the preload adjusters to do that. It is very hard for spring makers to make springs that are excatly the same length everytime, which is why adjustable spring perches are so nice, we can take into account the difference in free length with them. Also, your front springs are obviously different then your rear springs, so there is no reason I can think of that the spring perches (preload) should be adjusted to the same position.

03-22-2003, 11:41 AM
one more thing about the front damper adjustment, the rear springs ae softer then the fronts, is that enough to justify the difference in shock stiffness required??

03-22-2003, 10:21 PM
Originally posted by 240racer
one more thing about the front damper adjustment, the rear springs ae softer then the fronts, is that enough to justify the difference in shock stiffness required??

I think so.. They car is pretty loose with the rear springs they way they are. I think they car would be dorifto master with higher springs in the back.

Adjusting preload is what I was assuming I would have to do. I could raise the spring perches, and lower the mounting height so I gain stroke without increasing ride height.

I'm gonna put a ziptie on the back piston rod, and see if I really am hitting the bump stops.

03-24-2003, 06:45 PM
sounds like a good idea, let me know how it goes.