The rear suspension is the same as Factory Five offer as their "top of the range" option.
https://www.factoryfive.com/wp-conte...es-694x413.jpg
I THINK....The Harrison Cobras 'usually' have 350 lb front and 300lb rear.....but that is usually on live axle set ups.
( Maybe I'm wrong on that as well...'cause I've got
600lbs on the front , and 300lbs on the rear of my live axle Harrison Race Cobra...but that's not a NORMAL car. )
Now I don't have the detailed knowledge of how exactly all of the suspension is "worked out"...
but at least I can understand the way that the swinging arm of the Thunderbird IRS, has way more
leverage on the compression of the springs, and subsequently would take much stronger springs than for instance a live axle set up.
Obviously it's not just about how much weight is in any particular corner of the car, but depending on the angle of the spring/shock, combined with what leverage the swinging axle is applying because of where the spring shock sits within that swing range...then...i guess...there's a mathematical formula to work out the correct spring rate.
But HOW to work it out ....No bloody idea .
That's it....That's all I got !!
I might be completely wrong...happy for someone to tell me different.
Cheers,
Warren.