MUSTANGROB:  On level ground within normal limits and assuming a symmetrical steering and no slippage the turning radius is dependent only on the angle the steering wheels are turned.  In order for no slipping to occur, the outer turning wheel must have a slight toe-out in the turn.  This is to make sure that the turning wheels rotate about the same center.  The error of this center will cause slippage and will affect the turning radius slightly depending on the size of the error.

Regards
Dave

Yeah, ackerman steering must be assumed... and no weight transfer front to rear, to cause differences in backing vs. forward.  Would be negligible anyways.  I don't think castor matters either.. that would basically accounted for when checking the toe angle at full lock.

Here is site that might interest you based on your handle.
Checkout the Mustang Simulation Software,it lets you soup up you pony on the computer.  Then checkout the Tech Talk section for a lot of information about steering.  

http://www.auto-ware.com/