Bar Rate is the stiffness contribution of an anti-roll bar, expressed as the wheel-rate it adds when the two wheels on an axle move in opposite directions. It derives from the bar’s diameter, its lever arm length, the length of the torsion section and the material, and because torsional stiffness varies with the fourth power of diameter, small increases in bar size produce large rate changes. The defining property is that the bar adds roll stiffness without adding ride stiffness, since it produces no force when both wheels move together, which is why it is the preferred tool for adjusting balance without changing ride quality in two-wheel bump. That is only true for symmetric inputs, however, since in single-wheel bump the bar does add rate and transmits the input across the car, so an oversized bar buys balance at the cost of compliance over one-wheel bumps.