This formual will help you determine how much spring rate is gained or lost by adding or subtracting track - adding spacers, changing wheel offset...both of which affect motion ratio.

What the formula does not indicate, are changes due to offset which largely affect the length of the control arm. You must improvise. Lever arm calculations are linear, so don't worry about exponential errors, they will not exist.

This is part of a discussion under Track suspension setup by John Petrich. I thought this might be of some value...perhaps a sticky???

http://www.swayaway.com/Suspension%20Worksheet.htm

 

SUHweet link. Ah, the days of Sway-A-Way when I used to run aircooled VWs!!! Talk about handling improvements...

 

...those were scary, but not from first hand experience. Swing axles and a propensity for fires...both of which finally did a friends bug in. He did brag about it now and again, "it'll float you know." I'm sure floating it was on his mind after it burned up on the side of the road. He walked his anger off 16 miles later

 

Yeah, I had a swing-axle year model, but it had a built-up, close-ratio IRS tranny - oh, and 170 hp and some work to lighten 'er up... It was rather quick, let's say, and the front wheels didn't touch back down until well into 2nd gear... Made a mockery of many 5.0L 'Stangs back in the high school days... God, THAT was fun. Also handled well, thanks to being lowered, beefy Sway-A-Way stuff and excellent suspension parts and 205/50R15's... Top speed - 126 mph (closed course, yes) and yet still stable.

On the subject of fires - mechanical fuel pump location was not so good, and you had to be careful with routing fuel lines. However, the mechanical pump suffered vapor-lock issues in Texas heat and wouldn't support much more than 90hp, either. Definitely didn't supply enough fuel for my beastie!

 

Yea, I remember him being a wee bit pissy about the location of fuel lines