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I do like the idea of using a suspension analyser to work out how the geometry will function . A lot less guess work and you will get an idea of camber gain etc to get some performance out of your suspension
Having never done this or any other major suspension design before, Im excited to try it out. Messing around with the stock C5 pick-up points the analyzer shows that just narrowing it ~3", the geometry turns to sh!t. Im hoping to get both the front and rear optimized to work with the vehicle as best as I can
Having been down the path you are now on, I highly recommend you check out the following link:
http://www.lateral-g.net/forums/showthread.php4?t=42467 Ron Sutton is a genius when it comes to suspension design and he puts the concepts into very simple explanations. A couple things you should note about the C5 suspension is that, unlike old school thinking, the upper and lower control arms angle up (the UCA only slightly) toward the center of the car, producing a very long lateral instant center (swing arm) that actually limits excessive camber gain with travel. The second is that the lower control arm inner pick-up points are angled up toward the rear of the car. This helps produce caster gain with travel, which then translates into "good" camber gain when the wheels are turned. You are correct in noting that, as you narrow the suspension, the geometry changes. I ran into the same thing as I built longer control arms, and the geometry correction involved re-computing the heights of the pick-up points of the control arms to re-establish an acceptable instant center and roll center. I found it useful to do full-scale drawings starting with the roll center height I wanted to achieve at full suspension travel (the suspension height you anticipate during braking and cornering - mine is a high travel set-up limited by shock bump stops), then putting the data into Performance Trends to verify. Good luck with your project.
The following is in the "for what its worth" category and is how I approach defining the suspension pick-up points in a generic sense. It sounds complicated, but following your suspension program, it's not that bad. First, you have a few "hard" points already defined based on the spindle and tire width/backspacing you have chosen. Those are the wheel mounting flange height and depth, the lower ball joint center, and (subject to minor variation for camber adjustment), the upper ball joint center. Remember that the C5 suspension is designed for a deep backspace wheel to reduce scrub radius, so you will have to factor in things like wheel-well and fender lip clearance (especially at full compression) when you select your wheel. You need to be able to turn the wheel 27-30 degrees at full compression and roll. Do what you can to minimize scrub radius, but in the end, dynamic caster becomes more important. You know the C5 kingpin inclination angle (KPI), and your dynamic (at compressed height) caster should be 1.5 to 2 degrees greater than KPI for optimum cornering. The caster angle, the vertical location of the wheel centerline with respect to the centers of the upper and lower ball joints, and the fore-aft wheel centerline define the actual locations of the ball joints (the outer pivot points of the control arms). I enter the ball joint centers into the suspension program assuming compressed suspension height (i.e., with total caster at 1.5-2 degrees greater than KPI and initial camber at what I desire for pre-turn-in conditions. Remember, you will gain camber as the wheels are turned due to the caster. Then I would set my roll center at the height I want for a compressed suspension (1-2 inches -- less for road race, more for autocross). Roll center at ride height really doesn't mean much, it is the dynamic roll center that affects how the car handles. Draw a line from the center of the tire contact patch, through the roll center, inboard to a distance, let's say the same as the C5 (which is very long - 250 to 300 inches, or so). The inboard end of this line defines the lateral instant center point. Then draw a line from the upper ball joint center to the same instant center point. The control arm centerline inner pivot points fall on the two lines that run from the ball joints to the instant center at the appropriate control arm length. Realizing that you have defined the control arm pivots at their centerline, you still need to define the vertical location of each end of each control arm (front and rear). For these, I would start with the C5 relationships - upper control arm angled slightly down in the rear, lower control arm angled up in the rear. These angles define your anti-dive and the rate of caster gain during suspension travel. Raise the figure to ride height, and you can then see the control arm pick-up locations for fabrication. I actually build mock-up control arms out of scrap tubing and cheap ball joints so I can run the suspension through its travel and verify caster gain and the effects on camber at various turn angles. I also make all of my pick-up points adjustable so I can make minor tweaks later on if necessary. Hope this wasn't too confusing.
Pappy