suspension geometry (clean sheet design)

[dartslantsix]

I'm building an independent rear suspension for my Dart.
I'm down to designing my upper control arms, their length and mounting point.
My idea is to have two variables length of arm and angle in regard to the horizontal (mounting point). I wanted to make a spread sheet that I could run a bunch of different angles and lengths through and find the best roll center height and swing arm length.
Last night a wrote an equation to find swing arm length at ride height and I'm pretty sure I can also write one for roll center height. I can put these in the spread sheet and rock and roll. My problem is that I also need to find these values at full compression and full droop.
I'm not entirely sure how to describe the motion of the link mathematically. Thus being able to calculate the two values I need.
Short of drawing about a thousand scale drawings I'm kind of at a loss of how to do this.
Does anyone here know of a program that can handle this? Hopefully free?
Or other ideas of how to write equations for this?
I know I'm a geek, but I'd like to get this right.
Thanks for the help.

[MonzaRacer]

Honestly if I was going to do a IRS ( assume its going to be for a Chryco ,right?)I would look around at most of the designs and then mod them to look as good as you can and make the suspension work properly.
Doing clean sheet work is time consuming and if your not the educated guy your going to have a very long learning curve.
I personally have had great luck moding the pick up points and geometry from 89-up ford(sorry) Tbird /Cougar IRS.
We set one up from a junkyard with lots of custom parts and built a sweet 8.8 Center (but you could mod it to use a S60 dana 60 center by Strange.
Moser could probaly make up your axle shafts and look around at what the ricers are using in high horsepower cars. We had some very good luck as one fella made us new spindles in his machine shop class in a 5 axis CNC and we used a 3/4 tone hub/bearing from a GMC PU I think. The stubs were like 1 1/2 diameter and the CVs came from same 3/4 (I think) We did use a 12 bolt Chevy center(after we couldnt get proper stubs done for the 8.8) so we could take advantage of clips AND aclip eliminators too made from solid steel.
Honestly we had it made in about 4 weeks and it worked great .
With ART air springs it was flatan d we had vey little scrub or geometry change. The car was a mid 60s Abody,,,not sure of flavor.
The plan to build something form"clean sheet" we pondered and even worked al ot of math, big pain.
I even have several books somewhere on suspension design and lots of math books/knowledge. We had the set up on paper 3 times in a week and it took about 4 hrs each.
So I made the decision to check out stock stuff and mod apprpriately.
Dont be afraid to modifiy something over trying to make it.
I have a swing arm suspension in my 77 Monza and I am going to have to REDESIGN IT AGAIN ,if I keep it and I am designing the conversion kit for Hbody GM cars ,Monza/Vega, to run a "bolt in" 4 link. Its gonna take a lot more than I wnated in time.
Good luck and Turbo Cad would help. Trust me plotting points with out a CAD program takes time and nothing is free, if you want it done right save a few hundred buy a decnet cad program and learn it.
Lee

[dartslantsix]

I am using parts from a 93 T-bird supercoupe.
The subframe wouldn't fit under the Dart and it's too wide. So, I've built a new subframe and my lower control arms. The only thing left is upper control arms.
I'm just wanting to play with many different scenerios on the upper arms to get the best design. I think I've found a program that will allow this.
http://www.performancetrends.com/download.htm#rcc
I haven't got a chance to play with it yet though.
Thanks for the reply!

[pav8427]

PT works well and is worth the trial.Its easy to learn and will give you a lot of info.
To make it really worth it, be sure to have all(and then some) dimensions you think you might you need.

Hint; If you don't think you can get it done in the trial period, drop the trial on a disc and you can use it as long as you dump it on a different computer after the trial is up.

Doug