He is asking about toe-in or toe-out on the rear of an IRS car. It is all going to depend on your car and driving preferrence. It will fall somewhere between 1/4 in and 1/4 out; any more than that and you be scrubing speed, especially in a limited car like a 1600. I run mine at 0.
On a semi-trailing arm, the camber and toe change throughout the travel.
I just checked the toe on my design. When the arm is level, it is at zero toe.
As it progresses to bump, it gradually increases to .125" toe in.
As it progresses to droop, it gradually increases to .125" toe in.
If it continues to droop, the toe in continues to increase.
From bump to droop, the camber goes from negative, to zero, to slightly positive.
I think for my travel range I have ideal geometry. Any further comments?