Caster on an IRS

hey max i know we have been discussing front caster...is there any reason for caster in the rear.....i was lookin over my tbird irs and i noticed the lower rear control arms mounts are not parrallel with the frame...they actually come in towards the front of the car (when looking from the top)...the upper arm is perpendicular to the frame....if i understand the geometry correctly when the assemble articulates the lowers being at and angle to the frame owuld cause the bottom of the knuckle to kick forward therefore causing caster, correct? is there any reason to incorporate this into my design or could i just make the arm mounts parrallel to the frame therefore makin the arms perpendicular to the frame?

If I am understanding you correctly, it sounds to me that Ford is trying to generate a small ammount of anti-dive by designing the rear suspension to have caster loss when the suspension goes into bump. This will cause the suspension to compress under braking and lessen the dive effect of braking.

Other than that possibility, there really isn't a need for caster in rear suspension designs.

cool so i will just make all the arms come off the frame perpendicularly...thansk fro the response...you have been a giant help