The effect described by BenR in a way that is easy to relate to is that experienced when driving a city runaround hard. In which the roll stiffness of the front to rear can be made change in a way similar to uprating the front springs.
Going into a corner too fast leads, turning in induces the car to roll, somthing we are all familiar with, at a point in the corner all of a sudden the car will seem to understeer more, that is due to the front outside corner of the car to come to rest on its bumpstop. Therefore increacing the rollstiffness of the front. As the roll stiffness of the rear has remained the same an increace in the front roll stiffness induces this understeer.
If I would be right in saying that the roll stiffness cannot be adjusted using the torsion bar, it can be lowered but not stiffened then knowmatter what you do with the suspension (perhaps short of going really heavy with rear dampers, a dirty fix) a certain amount of understeer (relativly speaking) will be added over standard. This you may not notice due to the increaced speed at which you may be able to corner, i guess it all depends how you drive and why you want to lower your car. The balance of the car in my opinion may be negativly affected.
I have made some assumptions in what i have said so if i have made any errors someone please correct me. (i havent changed the suspension on my car due to these reasons, i currently enjoy the things that i am leaning to do with the rear end, I am a fan of oversteer, having just moved from a rear wheel drive car i am learning to drive again.)
