The purpose of anti-roll bars is two-fold. They control body roll in response to lateral acceleration, and MOST IMPORTANTLY, they "tune" the chassis' dynamic response - understeer or oversteer.

If you increase the size of the front bar, roll will decrease, but understeer will increase because you have added roll stiffness to the front so a greater proportion of total roll stiffness is at the front. If you increase the rear bar size alone, roll will be less, but the car may OVERSTEER due to increased rear roll stiffenss, without a corresponding change up front to maintain the original balance.

Roll stiffness contribution varies with the fourth power of bar diameter, so a small change should be quite noticeable. It's not a good idea to start swapping bars unless you have a good understanding of vehicle dynamics and chassis tuning.

Your best best is to find a front and rear bar "kit" from a performance aftermarket vendor. If none exists, then you can do your own development, if you feel you have the skills, or leave it alone.

Some body roll is desireable to give the driver feedback on where the car is in its performance envelope. High roll stiffness can make a car more responsive, but can also make a car "darty" and difficult to control.

Duke