Springs vs Barshttp://farnorthracing.com/autocross_secrets24.html
All of the elastic weight transfer must be taken up by the springs and bars - that's where it goes. The overall strength (in terms of roll resistance) of the total of the springs and bars determines the final roll angle of the sprung mass, and the relative strength front to rear determines balance. But the natural frequency of the suspension (which is calculated springs only) determines bump compliance, damping forces, and bump-related grip. If the springs get too stiff, then the wheel loses bump compliance and the car starts skating. So you choose springs to produce the natural frequency that gives you enough bump compliance, (normally not much higher than 2.5Hz for a non-aero car) and if those springs aren't enough to keep the roll angle under control, you have no choice but to go to bars.
If you are in this pickle (as will be most production-based cars: high CG, heavy sprung mass means lots of elastic weight transfer to absorb) you set the front springs for NF, the rear springs slightly stiffer (to keep the car flat as bumps move fore to aft; the rear must react a little faster). Bars you size so the total resistance gives you the roll angle you want but the relative resistance keeps the balance intact. For the typical nose-heavy production car, this means a stiff front bar and a soft rear bar. Done properly, you can dance on understeer/oversteer with small changes to the rear bar (and the rear bar is usually way easier to reach).
Ideally, you want no bars at all - while they don't create any extra weight transfer (the total amount of weight transfer is a function of track, CG height, and roll centre location) they can only add a larger proportion of roll resistance at that end of the car, which means increasing that end's share of the roll resistance, which in turn means "unsticking" that end of the car.
As a general rule, it is better to balance a car by figuring out ways to make the sliding end grip more rather than making the grippy end grip less. If the root cause is weight transfer, you may not have much choice - but the first instinct should not be to reach for the thicker bar.
A formula car can have bars the size of pencils totally as trim devices. For production car, getting the CG low and the sprung mass down can really pay grip dividends IF you remember to make the bars smaller as the car gets lighter.
This is a great site, and I've relied on his dynamics calculator in making changes to the Fiero. I am trying to rely on the springs to control suspension travel and the bar to tune the fore-aft balance. Right now my spring rate is twice what was considered optimal for the Fiero.
Another advantage(?) to stiffer springs is speeding up the weight transfer. My thinking was since TCR relies on slaloms (quick transitions) rather than sweepers (steady state turns), I want the weight transfer to happen quicker. This may be as much a preference thing, but it seems like it helps me adjust quicker. When the springs were softer it felt like I was needing to turn back for the next cone before the car was settled.
As to wheel rate, because the Fiero's front springs are so far inboard, I'm running 600 lb springs, but the wheel rate is about 200 lbs.