Comparing diameters only works in a very very general way. You are correct that as front weight goes down, the front bar rate needs to go down, or rear bar rate has to rise to maintain balance. BUT you need to be looking at total roll resistance at the front and rear wheels, not bar diameters. The roll center heights need to be taken into account, as RCH (roll center height) affects how much cornering load is automatically resisted by the geometry, and this load does not go through the bars. A higher RCH requires a lower bar rate.
To do all this requires suspension software with all suspension geometry points front and rear mapped out, and vehicle center of gravity height and F/R location, data. Info on anti-roll bar dia, arm length and mounting, where it connects to the suspension or frame, spring rates and the spring ratio to the wheels, corner weights. The software assumes a fixed amount of tire grip front and rear, so if your rear tires are larger than the front, the answers the software give you will be skewed.
Most aftermarket bars are not so stiff that you should think of reducing rates. The Pro-Touring crowd usually has a lot of tire under the car and this increases cornering load applied, you usually need some pretty large bars to resist it. I would try a normal aftermarket bar setup, then add more rear bar if you have understeer. That's what we did on our 73 Camaro we autocross and open track.
David
Last edited by David Pozzi; 12-24-2008 at 03:33 PM.
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